Absent in melanoma 2 regulates tumor cell proliferation in glioblastoma multiforme
Inflammation is a key aspect of glioblastoma multiforme (GBM) although it remains unclear how it contributes to GBM pathogenesis. Inflammasomes are intracellular multi-protein complexes that are involved in innate immunity and are activated by cellular stress, principally in macrophages. This study examined the expression of inflammasome-associated genes in GBM, particularly absent in melanoma 2 (AIM2).
Tissue samples from surgically-resected GBM tumors (n = 10) were compared to resected brain specimens from patients with epilepsy (age- and sex-matched Other Disease Controls (ODC, n=5)) by qRT-PCR, western blotting and immunofluorescence. Gene expression studies in human astrocytoma U251 cells were performed and the effects of deleting the absent in melanoma 2 (AIM2) gene using the CRISPR-Cas9 system were analyzed.
GBM tissues showed significantly elevated expression of multiple immune (CD3E, CD163, CD68, MX1, ARG1) and inflammasome (AIM2, NLRP1, IL18, CASP1, and IL-33) genes compared to ODC tissues, without induction of IL1B, IFNG or TNFA. An insert-containing AIM2 variant transcript was highly expressed in GBM tissues and in U251 cells. AIM2 immunoreactivity was concentrated in the tumor core in the absence of PCNA immunodetection and showed a predominant 52 kDa immunoreactive band on western blot. Deletion of AIM2 resulted in significantly enhanced proliferation of U251 cells, which also displayed increased resistance to temozolomide treatment.
GBM tumors express a distinct profile of inflammasome-associated genes in a tumor-specific manner. AIM2 expression in tumor cells suppressed cell proliferation while also conferring increased susceptibility to contemporary GBM therapy.
KeywordsGlioblastoma Inflammasome AIM2 Transcript insertion Temozolomide
EFB received a Victor Osten Summer Studentship from the Alberta Cancer Foundation (ACF). CP holds a Canada Research Chair in Neurological infection and Immunity. These studies were supported by the University Hospital Foundation (KP, CP).
PAC, GS, WGB, EFB and CP designed and executed the experiments as well as writing the manuscript. BAM and JF provided expert technical assistance and commentary on the manuscript. BMW, KP and FKHVL provided clinical care and advice on the manuscript. PAC, GS, EFB, WGB, BMW, KP, FKHVL and CP approved the final manuscript.
Compliance with ethical standard
The collection and use of brain tissues from all patients was approved (Pro0002291) by the University of Alberta Human Research Ethics Board (Biomedical) and written informed consent was received for all samples. This article does not contain any studies with animals performed by any of the authors.
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