Background and Discovery of WISP1
The gene for WISP1 was identified in a mouse mammary epithelial cell line and subsequently observed to modulate gastric tumor growth (Maiese 2014). The protein WISP1 is expressed in the epithelium, heart, kidney, lung, pancreas, placenta, ovaries, small intestine, spleen, and brain. WISP1 is a matricellular protein that alters the signaling of other pathways to affect programmed cell death, extracellular matrix production, cellular migration, and mitosis. WISP1 also can bind to leucine-rich proteoglycans that can affect the anchoring of cells to the extracellular matrix.
WISP1 is a target of the wingless pathway Wnt1. Wnt1 is a cysteine-rich glycosylated protein that can modulate multiple processes involving neuronal development, angiogenesis, immune cell modulation, tumorigenesis, and stem cell proliferation (Maiese et al. 2008). Wnt1 can be protective against toxic cellular environments. Activation of Wnt1 or its downstream signaling pathways can prevent cellular injury such as during experimental diabetes mellitus (DM), ischemic stroke, dopaminergic neuronal injury, inflammatory cell loss during neurodegenerative disorders, and neuronal synaptic dysfunction. During the downregulation of Wnt1 signaling, multiple detrimental processes can occur. These include the cell death of osteoblast progenitors and differentiated osteoblasts, injury of human monocytes, increased ethanol-induced oxidative stress on bone formation, impaired bone repair, progressive spinal cord injury, loss of neurogenesis, enhanced cardiac aging, blockade of cellular proliferation, inhibition of wound healing with fibroblast to myofibroblast transition, increased nitrosative stress during DM, loss of stem cell differentiation, promotion of programmed cell death, and defective placental development. Yet, the proliferative effects of Wnt1 can be detrimental as well especially in regard to the ability of Wnt1 signaling to promote tumor progression. Wnt signaling activity can increase chemotherapy tumor resistance through noncoding ribonucleic acids (RNAs) or through enhanced angiogenesis and may be a stimulus for numerous cancer disorders that include breast cancer and leukemia.
Signaling Pathways of WISP1
WISP1 governs multiple signal transduction pathways that can alter the proliferation, survival, and demise of cells that involves programmed cell death (Maiese 2015) (Fig. 1). WISP1 can control pathways of autophagy and apoptosis. WISP1 prevents apoptotic injury by inhibiting caspase activation (Wang et al. 2012). WISP1 also can block p53-mediated DNA damage to prevent the induction of apoptosis. In addition, WISP1 prevents phosphorylation of p38 mitogen-activated protein (MAP) kinase and c-Jun N-terminal kinase (JNK) and blocks c-Myc-mediated apoptosis.
In addition to pathways of programmed cell death, WISP1 oversees phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), the mechanistic target of rapamycin (mTOR), sirtuins, and forkhead transcription factors. In regard to PI 3-K and Akt, Akt is activated during increased WISP1 expression under conditions of cell injury such as during DNA damage, mechanical strain in osteoblasts, fibroblast proliferation in airway remodeling, cardiomyocyte injury vascular smooth muscle proliferation (Lu et al. 2016), oxidative stress, and Aβ exposure (Shang et al. 2013). Once Akt is activated, WISP1 phosphorylates and inhibits GSK-3β that prevents β-catenin from becoming phosphorylated, ubiquinated, and degraded. WISP1 during GSK-3β inhibition maintains the integrity of β-catenin and promotes the translocation of β-catenin to the nucleus in neurons, cardiomyocytes, hepatocytes, epithelial lung cells, and growth plate cartilage that can lead to tissue repair. β-catenin also can promote the expression of WISP1. WISP1 can prevent cell death primarily through inhibition of GSK-3β and apoptotic pathways with additional pathways that require inhibition of autophagy (Wang et al. 2012). Of note, WISP1 maintenance of β-catenin in some cases also can be detrimental and lead to tumor progression and metastatic disease (Knoblich et al. 2014) and be suggestive of a poor clinical prognosis during cancer diagnosis.
WISP1 can target several pathways of mTOR (Maiese 2015) by activating mTOR and phosphorylating p70 ribosomal S6 kinase (p70S6K) and the eukaryotic initiation factor 4E binding protein 1 (4EBP1) through the control of the regulatory mTOR component, the proline-rich Akt substrate 40 kDa (PRAS40). WISP1 controls PRAS40 by sequestering this protein in the intracellular compartment. WISP1 also oversees the posttranslational phosphorylation of AMP-activated protein kinase (AMPK) by differentially decreasing phosphorylation of tuberin (tuberous sclerosis 2) (TSC2) at Ser1387, a target of AMPK, and increasing phosphorylation of TSC2 at Thr1462, a target of Akt1 (Shang et al. 2013). WISP1 increases TSC2 activation by preventing activation of AMPK. When AMPK is active, it can phosphorylate TSC2 on serine1387 to ultimately inhibit the activity of mTOR and the mTORC1 complex. The ability of WISP1 to limit TSC2 (Ser1387) phosphorylation appears to allow WISP1 to increase the activity of downstream mTOR components, such as p70S6K. During β-amyloid (Aβ) exposure, WISP1 can phosphorylate mTOR, p70S6K, and 4EBP1 which are indicative of increased mTOR activity. However, during gene silencing of TSC2, phosphorylation of p70S6K is further enhanced during Aβ exposure alone and in the presence of WISP1, suggesting that inhibition of phosphorylation of the TSC2 (Ser1387) by WISP1 contributes to enhanced activity of the mTOR pathway (Shang et al. 2013). Yet, WISP1 also can increase TSC2 activity by promoting the Akt pathway through phosphorylation of TSC2 at Thr1462. Yet, it does appear that a minimal level of TSC2 activity is necessary to modulate WISP1 cytoprotection, since gene knockdown of TSC2 impairs the ability of WISP1 to provide cytoprotection (Shang et al. 2013).
Cytoprotection by WISP1 is also dependent upon sirtuin silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) and mammalian forkhead transcription pathways (Maiese 2014). WISP1 prevents SIRT1 caspase degradation and increases SIRT1 activity during oxidative stress to result in cellular protection. WISP1 also promotes SIRT1 nuclear translocation that is necessary for protection against apoptotic injury. WISP1 can directly control the posttranslational phosphorylation of the mammalian forkhead transcription factor FoxO3a by sequestering FoxO3a in the cytoplasm with protein 14–3-3 and limiting deacetylation of FoxO3a. WISP1 relies upon the inhibition of both FoxO3a and caspase activity during oxidative stress to block SIRT1 degradation. Overexpression of FoxO3a results in increased caspase 1 and caspase 3 activity during oxidative stress. WISP1 blocks FoxO3a activity through the inhibitory posttranslational phosphorylation of FoxO3a and inhibits caspase 1 and caspase 3 activation that would otherwise lead to SIRT1 degradation and apoptotic cell death.
WISP1 in Cellular Repair and Proliferation
As a proliferative agent, WISP1 can control stem cell proliferation, migration, and differentiation that ultimately may play a significant role in tissue repair (Fig. 1). WISP1 expression is upregulated during stem cell migration. WISP1 also is one of several components that control induced pluripotent stem cell reprogramming. WISP1 in conjunction with β-catenin is necessary for marrow-derived mesenchymal stem cell differentiation and oversees bone morphogenetic protein-3 (BMP-3)-stimulated mesenchymal stem cell proliferation (Cernea et al. 2016). WISP1 also can be differentially regulated during human embryonic stem cell and adipose-derived stem cell differentiation such that WISP1 expression is upregulated in human embryonic stem cells and repressed in adipose-derived stem cells during hepatic differentiation.
In the nervous system, WISP1 has been shown to promote cellular survival (Maiese 2015). WISP1 is necessary to provide protection to neurons by limiting the expression of the Bim/Bax complex, increasing the expression of Bclx(L)/Bax complex, and blocking mitochondrial cytochrome c release and caspase 3 activation (Wang et al. 2012). In regard to therapies directed against neurodegenerative disorders such as Alzheimer’s disease, WISP1 can protect central nervous system microglial cells against Aβ toxicity by controlling mTOR pathways that oversee PRAS40 and TSC2 (Shang et al. 2013) to increase mTOR activity. Through an autoregulatory loop, WISP1 can increase neuronal survival by limiting FoxO3a deacetylation, blocking caspase 1 and 3 activation, and fostering SIRT1 nuclear trafficking. As previously described, WISP1 prevents the phosphorylation and degradation of β-catenin to maintain the activity of β-catenin that can limit the induction of autophagy (Wang et al. 2012). In addition, WISP1 autoregulates its own expression that is dependent upon increased β-catenin activity (Wang et al. 2012).
Similar to the protection in the nervous system, WISP1 can promote vascular repair. WISP1 expression is selectively upregulated and can lead to vascular repair and regeneration following saphenous vein crush injury. WISP1 can improve cardiomyocyte survival (Shanmugam et al. 2011) and prevents cardiomyocyte cell death through PI3-K, Akt, and survivin pathways. WISP1 leads to vascular smooth muscle proliferation that may be important for tissue repair during injury but also may negatively impact restenosis following vascular grafting (Lu et al. 2016). However, WISP1 does not appear to lead to cellular proliferation in aging vascular cells.
In the musculoskeletal system, WISP1 plays a prominent role with bone development and repair (Maeda et al. 2015, Maiese 2016). WISP1 can increase osteogenesis through bone morphogenetic protein 2 (BMP-2), and bone formation through parathyroid hormone treatment can progress through WISP1 expression (Saidak et al. 2014). Bone formation following growth plate cartilage injury has been demonstrated to involve expression of the WISP1 gene. WISP1 leads to mesenchymal cell proliferation and osteoblastic differentiation with the repression of chondrocytic differentiation to enhance bone development and fracture repair. Yet, it is important to note that WISP1 may be considered a factor for the progression of osteoarthritis since WISP1 can result in chondrocyte hypertrophy through transforming growth factor-β signaling and activin-like kinase (ALK) 5. In addition, members of the CCN family including CCN4 are expressed to a greater extent in knee cartilage during osteoarthritis and rheumatoid arthritis when compared to normal controls.
In relation to DM and the control of cellular metabolism, WISP1 is one of several genes that is overexpressed during pancreatic regeneration, indicating that WISP1 may control stem cell development during DM. Expression of WISP1 also is increased during human adipocyte differentiation (Murahovschi et al. 2015). WISP1 expression is altered by weight change in humans and increases during insulin resistance in glucose-tolerant individuals (Murahovschi et al. 2015), suggestive that WISP1 may represent an important reparative process in individuals with DM. However, WISP1 expression has recently been linked to gestational diabetes with additional studies required to determine its role in this disorder (Sahin Ersoy et al. 2016).
During periods of trauma, WISP1 may be a vital factor during wound healing. WISP1 mRNA transcripts are upregulated during wound healing in models of third-degree burns, indicating that WISP1 may be a key element for tissue repair. WISP1 expression is upregulated during mechanical stretch injury of lung epithelial cells, and loss of WISP1 prevents mesenchymal transition necessary for the repair of lung epithelial cells. In addition, WISP1 that involves β-catenin/p300 may be required for epithelial cell repair during inflammatory lung injury (Zemans et al. 2013).
WISP1 in Tumorigenesis
Although WISP1 plays a prominent role during stem cell proliferation, musculoskeletal system development, and tissue repair following injury, as a proliferative agent and target of Wnt1, WISP1 also has a significant role in cancer (Fig. 1). Initial work demonstrated that WISP1 genomic DNA was amplified in colon cancer cell lines and in human tumors of the colon (Maiese 2014). A number of pathways may work in unison with WISP1 in cancer to promote cell cycle progression and tumor growth since increased expression of WISP1, Wnt1, survivin, and cyclin-D1 has been reported in colorectal cancer. Increased expression of WISP1 also may be indicative advanced progression of tumor cell growth, such as those associated with breast cancer (Klinke 2014) and esophageal squamous cell carcinoma. WISP1 has been associated with abnormal expression and gene fusion during lung adenocarcinoma (Yang et al. 2014). In addition, WISP1 expression is increased in neurofibromatosis type 1 tumorigenesis.
Under some conditions, WISP1 may be an important precursor for the development of cancer (Maiese 2014). There exists an association of WISP1 with chronic inflammatory bowel disease such as ulcerative colitis that may be a precursor for the development of gastrointestinal cancer. During chronic ethanol consumption, WISP1 has been implicated in hepatic cell proliferation that can lead to liver cancer (Mercer et al. 2014).
Variants of WISP1 may determine the degree that WISP1 fosters tumorigenesis. For example, variants of WISP1 have been described to be extremely aggressive in promoting cell growth in scirrhous gastric carcinomas and cholangiocarcinoma. Yet, non-variant WISP1 expression in lung cancer cells can be significantly less invasive, may limit lung metastases, and may block tumor cell invasion and motility. WISP1 expression may limit breast cancer growth and suppress melanoma growth during Notch1 activation since melanoma growth progresses during WISP1 gene knockdown (Shao et al. 2011). Yet, it is important to note that the ability of WISP1 to block metastatic disease may be tissue specific, since WISP1 expression in some experimental models has been shown to lead to early prostate cancer and distant bone metastatic disease (Ono et al. 2013).
WISP1, also known as CCN4, is a member of the CCN family of proteins and is expressed in multiple tissues that include the epithelium, heart, kidney, lung, pancreas, placenta, ovaries, small intestine, spleen, and brain. As a target of the wingless pathway Wnt1, WISP1 can govern pathways that can oversee musculoskeletal development, neuronal and cardiovascular cell survival, angiogenesis, immune cell modulation, cellular metabolism, tumorigenesis, and stem cell proliferation (Fig. 1).
WISP1 is intimately involved in a complex array of signal transduction pathways that involve PI 3-K, Akt, mTOR, SIRT1, and forkhead transcription factors. Each of these pathways control cellular mechanisms of proliferation and survival that rely upon p70S6K, 4EBP1, PRAS40, AMPK, TSC2, GSK-3β, β-catenin, and FoxO3a. WISP1 can regulate activity and posttranslation modification of proteins to determine the degree of activity of apoptotic and autophagic pathways that may ultimately determine clinical outcome.
During cellular repair and proliferation, WISP1 can differentially control stem cell proliferation, migration, and differentiation that can influence tissue repair. In the nervous system, WISP1 protects against both acute and chronic neurodegenerative disorders through the regulation of caspase activity, mitochondrial function, and Aβ toxicity. WISP1 also fosters cardiovascular repair during injury paradigms and may impact smooth muscle proliferation and vessel restenosis during vascular grafting. In the musculoskeletal system, WISP1 promotes mesenchymal cell proliferation and osteoblastic differentiation to increase bone development and repair fractures, but WISP1 also may have a prominent role during the development of osteoarthritis and rheumatoid arthritis. In relation to cellular metabolism, WISP1 may be important for pancreatic regeneration and insulin resistance during DM. In addition, WISP1 has been shown in models of tissue injury and trauma to be vital for wound healing.
However, as a proliferative agent and a target of Wnt1, WISP1 plays an important role during tumorigenesis. WISP1 can function with several pathways such as Wnt1, survivin, and cyclin-D1 to promote cell cycle progression and tumor growth. Under some inflammatory conditions, WISP1 also may be an important precursor for the development of cancer. Variants of WISP1 may determine the degree that WISP1 fosters cancer progression and non-variant WISP1 expression in cancer cells can be less invasive and limit metastatic disease.
WISP1 offers exciting prospects for the development of novel strategies against acute and chronic disorders that may involve cellular metabolism as well as the nervous, musculoskeletal, cardiac, pulmonary, and vascular systems. At the cellular level, WISP1 alters the signaling of other pathways to affect programmed cell death, stem cell development and differentiation, extracellular matrix production, cellular migration, and mitosis. Further understanding of the intimate relationship WISP1 holds with multiple proliferative and reparative pathways will be necessary for the successful development of WISP1 as an effective and safe clinical target for multiple disorders.
This research was supported by the following grants to Kenneth Maiese: American Diabetes Association, American Heart Association, NIH NIEHS, NIH NIA, NIH NINDS, and NIH ARRA.
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