Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi

NMT (N-Myristoyltransferase)

  • Umashankar Das
  • Joel Howlett
  • Sujeet Kumar
  • Sreejit Parameswaran
  • Anil Sharma
  • Jonathan R. Dimmock
  • Rajendra K. Sharma
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_538

Synonyms

Historical Background

Lipid modification is one of the most common posttranslational modifications in eukaryotic cells that take place either at or near the amino terminus or the carboxy terminus of the proteins (Resh 2013). This process is sequence specific and classified as myristoylation, palmitoylation, prenylation, and glycosylphosphatidylinositol according to the identity of the attached lipid. The structural changes resulting from these modifications have effects on the stability, cellular location, and biological activity of the proteins (Resh 2013). These processes are becoming increasingly important for the study of cancer, as several key oncoproteins require this type of “posttranslational maturation” for their biological activity and for their ability to transform cells. Among these lipid modifications, protein myristoylation is known to be very important which refers to the covalent attachment of myristate, a 14-carbon saturated fatty acid, to the N-terminal glycine residue of a number of eukaryotic proteins (Rajala et al. 2000a). Protein myristoylation is catalyzed by the enzyme myristoyl CoA:protein N-myristoyltransferase, which is ubiquitously distributed among eukaryotes including humans (Rajala et al. 2000a; King and Sharma 1992). This enzyme often exists as isoforms and is very specific for the transfer of myristate in vivo (Rajala et al. 2000a). Myristoylation occurs in at least 0.5% of eukaryotic proteins suggesting an important role in the growth and survival of cells whereas myristate is <1% of the fatty acid pool (Resh 2012).

N-myristoyl transferase (NMT) exists in two major isoforms NMT-1 and NMT-2 in all mammalian species, both of which are highly conserved (Giang and Cravatt 1998). NMT-1 and NMT-2 have an overall sequence identity of 76–77% with most divergence being at their N terminus (Giang and Cravatt 1998). While NMT-2 appears as a single 65 kDa protein, NMT-1 exists as four distinct isoforms ranging from 49 to 68 kDa in size (Giang and Cravatt 1998). The smaller isoform of 416 amino acids is catalytically active and there is no functional requirement for the longer isoform. The extended N-terminus is located close to the myristoyl-CoA binding site as well as the peptide-binding site suggesting that this region plays an important role in the coordinated control of the catalytic activity of NMT-1 (Kumar and Sharma 2015). The N-terminal extensions of the human NMT-1 may also play a role in targeting the enzyme to ribosomes. A recent observation is that the N-terminal region in the catalytic module of NMT-1 functions as a regulatory control segment (Kumar and Sharma 2015). A comparison of the activity of NMT1 and NMT2 toward a small panel of substrate peptides in in vitro experiments reveals that the isozymes have similar, but distinguishable relative selectivity (Kumar and Sharma 2015). It was found that NMT-2 is not active in embryonic stem cells but its level increases during development. The distribution of both isozymes is found in normal tissue. The selective knockdown of the expression of NMT1, NMT2, or both isozymes in human colon cancer HT-29 cells and ovarian carcinoma SKOV-3 cells using small interfering RNAs (siRNA) shows that siRNA sequences unique to each NMT message selectively reduce the expression of the NMT1 or NMT2 isozyme by >90% for at least 72 h and had shown that NMT1 and NMT2 have both redundant and unique effects on protein processing, apoptosis, and cell proliferation (Ducker et al. 2005). Protein modifications have been identified to play essential roles in various oncogenic proteins and modified signal transduction pathways of cancer (Selvakumar et al. 2007). Myristoylation of proteins is known to be involved in the pathogenesis of cancer (Selvakumar et al. 2007). Consequently, NMT has been proposed as a molecular target in anticancer drug design (Das et al. 2012).

The Role of N-Myristoyltransferase in Cancers

Colon Cancer

NMT was found to be involved in the posttranslational modification of c-Src and also overexpressed in colon tumor cells (Selvakumar et al. 2007). Inhibition of Src myristoylation in colon cancer cell lines prevents the localization of the kinase to the plasma membrane, resulting in decreased colony formation and cell proliferation (Shoji et al. 1990). As NMTs and Src are overexpressed in colonic tumors (Selvakumar et al. 2007), NMT inhibitors have a potential role to play in colon cancer therapeutics.

An elevated level of NMT activity in the azoxymethane-induced rat model of colonic tumors was observed when compared with normal-appearing adjacent mucosa and normal mucosa (Table 1) (Magnuson et al. 1995). However, polyps and tumors of stage B1 had the highest NMT activity (Table 2). These observations suggest that NMT activity is elevated during the early stage of colonic carcinogenesis. It is noteworthy that elevated NMT activity was also observed in all these adenocarcinomas and was predominantly found in the cytosolic fraction (Magnuson et al. 1995). Elevated NMT activity was observed close to the rectum which is an area that carries a poor prognosis in cancer (Magnuson et al. 1995). Furthermore, NMT activity was evaluated in Crohn’s disease colons or volvulus and found to be similar to normal mucosa, suggesting that NMT is specific to neoplastic cells and not to cells undergoing inflammatory or non-cancerous changes (Magnuson et al. 1995).
NMT (N-Myristoyltransferase), Table 1

N-Myristoyltransferase activity in colonic mucosal homogenates and azoxymethane-induced rat colonic tumors (Magnuson et al. 1995)

Tissue

No.

N-Myristoyltransferase activitya

U/mg protein

U/g tissue

Normal mucosa from control rats

3

0.34 ± 0.02

7.76 ± 0.89

Normal-appearing mucosa from rats given injections

7

0.43 ± 0.08

8.86 ± 1.86

Colonic tumors

35

1.69 ± 0.15b

47.99 ± 5.06b

aMean ± SE

bSignificant difference from normal and normal-appearing mucosa (P < .05)

NMT (N-Myristoyltransferase), Table 2

N-Myristoyltransferase activity in azoxymethane-induced rat colonic tumors (Magnuson et al. 1995)

Tumor stage

No.

N-Myristoyltransferase activitya

U/mg protein

U/g tissue

Adenomatous polyp

5

2.32 ± 0.38

60.43 ± 12.5

A

8

1.39 ± 0.20

31.19 ± 5.67

Bl

10

2.11 ± 0.32

65.39 ± 12.59

B2

10

1.35 ± 0.02

40.80 ± 6.52

C2

2

0.90 ± 0.43

33.03 ± 15.09

aMean ± SE

Elevated NMT activity during carcinogenesis may be due to the higher demand for myristoylation of various proteins/oncoproteins (src, ras, etc.) which are overexpressed and activated during tumorigenesis. Among several proteins in the intestine that are myristoylated, tyrosine kinases of the src family are the most studied. The levels of the myristoylated tyrosine kinases, pp60c-src and pp60c-yes, are several folds higher in colonic preneoplastic lesions and neoplasms compared with normal colon cells (Selvakumar et al. 2007). Differential expression of pp60c-src has been observed in colonic tumor-derived cell lines (Selvakumar et al. 2007) and in colonic polyps prone to developing cancer (Selvakumar et al. 2007). Higher levels of cytoskeletal-associated pp60c-src protein tyrosine kinase activity have been observed in intestinal crypt cells along with higher expression of pp60c-yes in the normal intestinal epithelium. Studies have revealed that pp60c-src is overexpressed in human colon carcinoma and it has enhanced kinase activity in progressive stages and metastases of human colorectal cancer (Selvakumar et al. 2007). In colonic cell lines, blockage of pp60c-srcN-myristoylation results in depressed colony formation and reduced proliferation (Magnuson et al. 1995). Earlier, it has been shown that src kinase activity is positively regulated by myristoylation and the nonmyristoylated c-Src exhibited reduced kinase activity (Raju et al. 1997).

An elevated expression of NMT in colon cancer cell lines was observed which correlates with high levels of c-Src (Giang and Cravatt 1998). The overexpression of NMT in colorectal cancer has implications with regard to the development of chemotherapeutic agents. However, from the above study it is not clear whether there is an increase in the production of NMT or the increased activity is due to a conformational change in the pre-existing enzyme. In addition, the increased NMT activity may be due to the removal of an inhibitor or the presence of an activator. Therefore, the expression of NMT in normal colonic mucosa and adenocarcinomas from human colorectal surgical specimens were studied by immunoblotting and its localization was further confirmed by immunohistochemistry (Raju et al. 1997). In both normal mucosa and colorectal adenocarcinoma, NMT-1 with a molecular mass of 48.5 kDa was identified when probed with an antihuman NMT antibody (Fig. 1a). These findings were further confirmed by immunohistochemical studies which showed stronger cytoplasmic localization in colorectal adenocarcinomas compared to normal colonic mucosa. In addition the mucosal sections taken distant from the tumor showed only a mild reactivity (Fig. 1b). The transitional mucosa in the vicinity of the cancers did, however, stain more than normal mucosa albeit not to the same degree as the tumors (Fig. 1c).
NMT (N-Myristoyltransferase), Fig. 1

Western blot analysis of N-myristoyltransferase. (a) normal colorectal mucosa tissue and columns 1–6, colorectal tumor tissue samples; quantitative analysis of the NMT-1 protein band (see arrow) from Western blot was carried out using Imaging software (NIH at http://rsb.info.nih.gov/nih-image/download.html); (b) expression of NMT in colorectal adenocarcinoma in normal mucosa far removed from tumor showing a mild degree of focal staining (see arrows), and (c) transitional mucosa showing a mild to moderate degree of diffuse reactivity compared to the strong tumor reactivity on the right (Raju et al. 1997)

Since NMT is most abundant in the colon cancer tissue, a limitation of assessing the activity and protein expression of NMT for prognostic/diagnostic purposes is difficult because endoscopic biopsy must be performed to obtain the tumor tissue. An investigation of blood samples from colorectal cancer bearing rats and cancer patients in our laboratory showed that the NMT activity in the peripheral blood mononuclear cells (PBMC) of tumor bearing rats was significantly higher compared to PBMC control rats (Fig. 2) (Shrivastav et al. 2007b). NMT activity was also higher in the bone marrow of tumor bearing rats compared to normal bone marrow (Fig. 2). However, the highest activity was observed in the bone marrow macrophages of tumor-bearing rats (Fig. 2a). In addition, Western blot analysis studies revealed that there is overexpression of NMT-1 in the PBMC and in the bone marrow of tumor bearing rats compared to that of control rats (Fig. 2b).
NMT (N-Myristoyltransferase), Fig. 2

N-myristoyltransferase activity in peripheral blood mononuclear cells (PBMC) and bone marrow cells (BMC) of normal and colorectal tumor bearing rats. (a) Isolated PBMC from peripheral blood of control or tumor bearing rat were assessed for NMT activity. Values are mean ± SD of three independent experiments. (b) Western blot analysis of PBMC and BMC of normal and colorectal tumor bearing rats (Shrivastav et al. 2007b)

Furthermore, immunohistochemical analysis revealed weak to negative staining for NMT-1 in PBMC of controls (Fig. 3a, b) whereas strong positivity was observed in the PBMC of colon cancer patients (Fig. 3c, d). We also observed that NMT-1 remained cytoplasmic in the control bone marrow mononuclear cells (Fig. 4a) whereas NMT-1 localized mostly in the nuclei of the bone marrow mononuclear cells of colon cancer patients (Fig. 4b). The difference in NMT-1 expression and its altered localization in the bone marrow of the tumor bearing host suggests that NMT-1 is a potential novel marker for diagnostic purposes.
NMT (N-Myristoyltransferase), Fig. 3

Immunohistochemical analysis of PBMC of normal and colon cancer patients. (a) negative staining of lymphocytes (see arrow); (b) shows negative staining of monocytes (see arrows) in peripheral blood smear of control; (c) peripheral blood smear of colon cancer patients show positive staining of macrophages (arrows) and (d) peripheral blood smear of colon cancer patients show positive staining of neutrophil (fat arrows), lymphocyte (lean long arrow), and macrophages (arrow) (Shrivastav et al. 2007b)

NMT (N-Myristoyltransferase), Fig. 4

Immunohistochemical analysis of bone marrow of normal and colon cancer patients. (a) NMT staining is mostly cytoplasmic in bone marrow of control (see arrow); (b) intense nuclear (and some cytoplasmic) staining for NMT is observed in the bone marrow of colon cancer patient (see arrow) (Shrivastav et al. 2007b)

Our laboratory had reported for the first time a high expression of NMT-2 in human colorectal tumors compared to normal tissues (Fig. 5a) (Selvakumar et al. 2006). The quantitative analysis demonstrated a significant increase in NMT-2 expression in human colorectal tumor tissues compared to normal mucosa (Fig. 5b). However, higher expression of NMT-2 was observed in polyps (Fig. 5, lanes P1 and P2). Furthermore, we observed the expression of NMT-2 in various human colon cancer cell lines (Colo320, SW480, SW620, HT29, DLDI, WiDr, HCT15, and HCT116). It is interesting that NMT-2 expression was higher in Colo320 cells compared to other cell lines (Fig. 5c). However, the expression of NMT-2 in HCT15 was poorly observed (Fig. 5c). These results indicate that the NMT-2 gene is upregulated during molecular events that take place during the malignant formation of colon cancer. The higher expression of NMT-2 was also reported in rat hepatoma cells by dioxin toxicity and the inducible level of NMT-2 was a direct consequence of Ah receptor activation [8] (Selvakumar et al. 2007).
NMT (N-Myristoyltransferase), Fig. 5

Western blot analysis of N-myristoyltransferase-2 in human colorectal carcinoma. (a) Western blot analysis of human colorectal polyps (lanes P1, P2), normal (N), and tumor tissue (C). (b) Quantitation analysis of Western blot analysis was carried out using image software (NIH at http://rsb.info.nih.gov/nih-image/download.html). The data presented are representative of at least three separate experiments. Statistical significance was determined using Student t test analysis; *P < 0.05. (c) Western blot analysis of various human colon cancer cell lines (Selvakumar et al. 2006)

Gallbladder Carcinoma

We reported for the first time that NMT-1 and NMT-2 protein expression is higher in colorectal adenocarcinomas than the adjacent nonmalignant mucosa (Raju et al. 1997; Shrivastav et al. 2007; Selvakumar et al. 2006). Then we extended our investigation on NMT expression in human gallbladder carcinoma (Rajala et al. 2000b). Gallbladder carcinoma is a rare yet often fatal cancer. Over 90% of gallbladder carcinomas are adenocarcinomas. Advanced local and regional disease is usually present at the time of diagnosis (Rajala et al. 2000b). When we analyzed gallbladder carcinoma cases, 60% of the gallbladder carcinomas demonstrated moderate to strong cytoplasmic positive for NMT in the invasive carcinoma with increased intensity in the invasive component, while 40% of the cases were observed as negative. The in situ component demonstrated that the cytoplasmic staining was from mild to moderate in 67% of the cases whereas normal gallbladder mucosa revealed weak to negative cytoplasmic staining (Fig. 6).
NMT (N-Myristoyltransferase), Fig. 6

Expression of N-myristoyltransferase in gallbladder mucosa. (a) normal mucosa; (b) with weak positive staining; (c) carcinoma in situ with moderate staining; (d) papillary carcinoma with moderate staining; (e) invasive carcinoma with strong positive staining and negative overlying mucosa and (f) higher power of invasive carcinoma (Rajala et al. 2000b)

The increased expression of NMT in p53 mutant cases suggested that wild-type p53 may have a negative regulatory effect on NMT gene expression. NMT has been shown to be associated with a ribosomal subcellular fraction. The incidence of gallbladder carcinoma is higher in older age groups suggesting that hormonal imbalance may play a major role (Rajala et al. 2000b). Previous studies of prostate carcinoma indicate the greater abundance of NMT mRNA in hormone refractory cells than in hormone sensitive cells (Selvakumar et al. 2007). Src proteins of hormone sensitive cells were exclusively cytoplasmic, consistent with an absence of myristoylation, and suggested a regulatory role of hormones in NMT regulation (Selvakumar et al. 2007). Isolation of the NMT promoter and transfection studies in gallbladder cell lines would give a better understanding of the transcriptional regulation of NMT expression. Moderate to strong p53 staining was observed in 63% of the cases of the in situ components and 80% of the invasive components. Though the in situ staining of p53 was unrelated to the clinical outcome, moderate to strong staining of the invasive component as observed in 50% of the cases was associated with a mean survival time of 8.8 months. Our study shows that tumors with increased expression of p53 and NMT were associated with poor clinical outcomes as evidenced by their mean survival times. However, such a trend should be evaluated in larger numbers in order for this premise to be considered an independent prognostic marker. Since we observed a high expression of NMT in rat, human colon cancer, and human gallbladder cancer, we further investigated this enzyme expression in human brain tumors.

Brain Tumors

Brain tumors are the most common malignant solid tumor in childhood, and the incidence among adults is slightly higher in males than the females (∼3.7 and ∼2.6 per 100,000 males and females, respectively). The long-term disease free survival for children and adults with highly malignant brain tumors is poor. c-Src is a substrate for NMT and is known to be activated/overexpressed in various cancers and is increased in human malignant gliomas (Selvakumar et al. 2007). We reported for the first time a high NMT activity as well as protein expression of NMT-1 and NMT-2 in human brain tumors (Lu et al. 2005). Glial-derived neoplasms (gliomas) are the most aggressive brain tumor type, and account for 44% of all primary brain tumors. The most aggressive glial neoplasm is glioblastoma multiforme and this tumor type accounts for more than half of the primary brain tumors diagnosed in North America (Selvakumar et al. 2007; Lu et al. 2005).

At the present time, for diagnostic purposes, brain tumor sections stained with hematoxylin and eosin and an array of immunohistochemical stains using glial and neuronal marker proteins (glial fibrillary acidic protein, neuronal specific enolase, etc.) are scrutinized and categorized by light microscopy. Identification of tumor cells for diagnostic purposes is currently largely limited to light microscopy at the cellular level. Interestingly, we observed higher NMT activity in WHO grade 1 patients compared with others of higher WHO grades (Fig. 7a, lanes 5–9 vs lanes 10, 11). These observations were further supported by Western blotting using monoclonal antibodies against NMT-1 and NMT-2 and suggested both forms of NMT (NMT-1 and NMT-2) protein expressions were observed when compared to normal brain tissues (Fig. 7b). It revealed that these genes are upregulated as part of a series of molecular events that take place during carcinogenesis in the brain. Earlier it has been reported that the ubiquitous form of pp60c-src was expressed in malignant human glioma cell lines (Selvakumar et al. 2007). In anaplastic astrocytoma biopsy samples, focal adhesion kinase (FAK) is expressed and the activity of Src kinase is elevated as is the activity of Src kinase associated with FAK (Selvakumar et al. 2007). C-yes (proto-oncogenepp62c-yes) activities and protein levels were elevated in human melanoma and melanocyte cell lines (Selvakumar et al. 2007). Since these proteins were shown to be elevated in human glioma and melanoma cell lines (Selvakumar et al. 2007), it follows that N-myristoylation is required in order to facilitate the biological functions. This upregulation in gene expression suggests a role in the carcinogenic pathway as well as a possible therapeutic target for future study.
NMT (N-Myristoyltransferase), Fig. 7

N-myristoyltransferase activity and Western blot analysis of NMT in human brain tumor samples. (a) NMT activity; lanes 1–3, normal human brain tissue; lane 4, not WHO graded; lanes 5–9, WHO grade 1; lane 10, WHO grade 2; lane 11, WHO grade 4. The data were expressed as the mean ± SD of three samples in each group. (b) Western blot analysis of NMT-1 and NMT-2 in brain tumor tissue. Lanes 1–3, normal human brain tissue; lane 4, not WHO graded; lanes 5–9, WHO grade 1; lane 10, WHO grade 2; lane 11, WHO grade 4 (Lu et al. 2005)

Oral Squamous Cell Carcinoma

Currently, oral squamous cell carcinoma (OSCC) is the most prevalent malignant neoplasm of the head and neck region. The recent increases in these numbers are attributed to the human papilloma virus (types 16 and 18) (Selvakumar et al. 2007), associated cancers of the tonsils and base of the tongue. Since increased expression and activity of NMT in various cancers suggest its involvement in carcinogenesis, we investigated the presence of NMT in oral cancer. Previously, it had been reported that NMT activity is found to be 2.5 fold greater in cancerous tissues over normal tissue samples from the same patient (Shrivastav et al. 2007a). In the same study, NMT was found in nuclear and cytoplasmic localizations in tumor samples compared to normal samples where the enzyme is primarily cytoplasmic (Shrivastav et al. 2007a). It is known that NMT will redistribute to the nucleus in ischemic cardiac cells under stress (Rajala et al. 2002). Epithelial cells involved in OSCC undergo a similar stress response with increasing tumor load, possibly providing an explanation for nuclear-bound NMT (Shrivastav et al. 2007a). The increased NMT activity could be due to the increased demand for myristoylation of oncoproteins and other diverse proteins involved in the multistep process of oncogenesis (Selvakumar et al. 2007). Myristoylated tyrosine kinases pp60c-src and pp60c-yes are known to be elevated in carcinomas of the colon, possibly creating an increased demand for NMT (Selvakumar et al. 2007). Secondly, atypical myristoylation of proteins which are not normally myristoylated could occur as a result of neoplastic changes (Selvakumar et al. 2007). This has been demonstrated with the protein p21 Ras, which results in transformation activity or with H-Ras and K-Ras where cellular localization and MAP kinase activation are affected (Selvakumar et al. 2007). It is still unknown how early overexpression of NMT occurs in OSCC but there is the potential for a role as a biomarker for diagnosis and the possibility as a targeted therapeutic agent.

Breast Cancer

A correlation has been established between NMT activity in mammary epithelial cells and proliferative ability (Clegg et al. 1999). Immunohistochemical analysis of grades 1, 2, and 3 ductal carcinomas of the breast cancer tissue array display a stepwise increase in staining (Shrivastav et al. 2009). While these tissues showed strong staining, normal breast tissue displays low or negative staining (Shrivastav et al. 2009). Furthermore, immunohistochemical analysis was carried out in breast cancer patients and revealed NMT positivity for malignant breast tumor whereas no or low NMT staining was observed in normal breast tissue (Table 3). Src, a substrate for N-myristoylation, has been observed to be 4–20 folds higher in breast cancer tissue when compared to controls (Selvakumar et al. 2007). Therefore it is possible that the overexpression of NMT is due to the high demand of the myristoylation of Src. NMT could prove to have overlapping functions and NMT-1 is critical for tumor cell proliferation suggesting that isoform-specific inhibitors could be a viable biomarker in the diagnosis of breast cancer.
NMT (N-Myristoyltransferase), Table 3

Summary of NMT positivity in female breast cancer (Shrivastav et al. 2009)

Age (years)

Pathology diagnosis

Grade

Type

Positivity (%)a

Intensitya

ERb

60

IDC NOSc

II

Malignant

>75

Strong

_

40

IDC NOS

I

Malignant

15–20

Moderate

+

52

IDC NOS

I

Malignant

35–50

Strong

_

38

IDC NOS

II

Malignant

>75

Strong

_

51

IDC NOS

II

Malignant

>75

Moderate

_

64

IDC NOS

III

Malignant

>75

Strong

_

48

IDC NOS

II

Malignant

>75

Strong

+

38

Medullary carcinoma

_

Malignant

50–75

Strong

_

49

Medullary carcinoma

_

Malignant

15–20

Weak

+

58

Mucinous adenocarcinoma

_

Malignant

50–75

Strong

_

54

Apocrine carcinoma

_

Malignant

35–50

Strong

_

60

Fibro-fatty tissue of No 01

 

Normal

_

Negative

_

38

Breast tissue of No 36

_

Normal

_

Negative

_

58

Breast tissue of No 38

_

Normal

5–10

Weak

+

54

Breast tissue of No 40

_

Normal

_

_

+

aNMT

bEstrogen receptor staining (ER)

cIDC NOS infiltrating ductal carcinoma, not otherwise specified. Immunohistochemical staining results were evaluated in a semiquantitative manner as follows: number of breast cancer cells positive: rare (1–5); 5–10%; 15–25%; 25–35%; 35–50%; 50–75%; >75%. Staining intensity was evaluated as negative, weak, moderate, or strong. Grade I or well-differentiated: cells appear normal and are not growing rapidly. Grade II or moderately differentiated: cells appear slightly different from normal. Grade III or poorly differentiated: cells appear abnormal and tend to grow and spread more aggressively (Shrivastav et al. 2009)

NMT Inhibitors as Cytotoxic Agents

Anticancer properties of various structurally diverse NMT inhibitors have been reviewed (Das et al. 2012). Among them, N-heterocyclic benzenesulphonamides have shown remarkable NMT inhibitory as well as anticancer properties. Recently a selective NMT inhibitor (Selvakumar et al. 2007) which was originally discovered as an inhibitor of Trypanosoma brucei NMT demonstrated dose-dependent inhibition of N-myristoylation that is cytotoxic in a time-dependent manner in HeLa cells (Fig. 8) (Thinon et al. 2016). Inhibition of N-myristoylation had resulted in a complete killing of HeLa cells. NMT inhibition in HeLa cells show that cells die through apoptosis following or concurrent with accumulation in the G1 phase. In this study, a quantitative proteomics analysis to map protein expression changes for more than 2700 proteins in response to treatment with the NMT inhibitor in HeLa cells showed that downregulation of proteins involved in cell cycle regulation and upregulation of proteins involved in the endoplasmic reticulum stress and unfolded protein response, with similar results in breast (MCF-7, MDA-MB-231) and colon (HCT116) cancer cell lines.
NMT (N-Myristoyltransferase), Fig. 8

The structure of NMT inhibitor showing potent cytotoxic properties

Summary

Protein myristoylation is a key biochemical process which plays an important role in the functioning of many cell proteins. Our extensive studies on NMT activity and expression in different human cancers reveal that NMT is over expressed in cancer cells compared to nonmalignant cells. These results demonstrate the role and significance of protein myristoylation in various cancers and had triggered our interests in developing NMT as a diagnostic marker. NMT inhibitors have shown potent anticancer properties which warrant their potential as future anticancer drugs. In the light of these results, further studies are required to examine a wide range of other tumors and the corresponding normal tissues for NMT activity to support the role of NMT in tumor progression. Secondly, indepth investigation of the role of NMT-1 and NMT-2 in tumorigenesis will contribute to further understanding of the mechanisms of tumor progression. In conclusion, the development of NMT inhibitors as future anticancer drugs warrants substantial potential which needs further research.

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© Springer International Publishing AG 2018

Authors and Affiliations

  • Umashankar Das
    • 1
  • Joel Howlett
    • 2
  • Sujeet Kumar
    • 2
  • Sreejit Parameswaran
    • 2
  • Anil Sharma
    • 3
  • Jonathan R. Dimmock
    • 1
  • Rajendra K. Sharma
    • 2
    • 4
  1. 1.Drug Discovery and Development Research Group, College of Pharmacy and NutritionUniversity of SaskatchewanSaskatoonCanada
  2. 2.Department of Pathology and Laboratory Medicine, College of MedicineUniversity of SaskatchewanSaskatoonCanada
  3. 3.ENT clinicSaskatoonCanada
  4. 4.Cancer Research Unit, Saskatchewan Cancer AgencySaskatoonCanada