FAM96A is a novel pro-apoptotic tumor suppressor in gastrointestinal stromal tumors

Abstract

The ability to escape apoptosis is a hallmark of cancer-initiating cells and a key factor of resistance to oncolytic therapy. Here, we identify FAM96A as a ubiquitous, evolutionarily conserved apoptosome-activating protein and investigate its potential pro-apoptotic tumor suppressor function in gastrointestinal stromal tumors (GISTs). Interaction between FAM96A and apoptotic peptidase activating factor 1 (APAF1) was identified in yeast two-hybrid screen and further studied by deletion mutants, glutathione-S-transferase pull-down, co-immunoprecipitation and immunofluorescence. Effects of FAM96A overexpression and knock-down on apoptosis sensitivity were examined in cancer cells and zebrafish embryos. Expression of FAM96A in GIST and histogenetically related cells including interstitial cells of Cajal (ICCs), ‘fibroblast-like cells’ (FLCs) and ICC stem cells (ICC-SCs) was investigated by Northern blotting, reverse transcription—polymerase chain reaction, immunohistochemistry and Western immunoblotting. Tumorigenicity of GIST cells and transformed murine ICC-SC stably transduced to re-express FAM96A was studied by xeno- and allografting into immunocompromised mice. FAM96A was found to bind APAF1 and to enhance the induction of mitochondrial apoptosis. FAM96A protein or mRNA was dramatically reduced or lost in 106 of 108 GIST samples representing three independent patient cohorts. Whereas ICCs, ICC-SCs and FLCs, the presumed normal counterparts of GIST, were found to robustly express FAM96A protein and mRNA, FAM96A expression was much reduced in tumorigenic ICC-SCs. Re-expression of FAM96A in GIST cells and transformed ICC-SCs increased apoptosis sensitivity and diminished tumorigenicity. Our data suggest FAM96A is a novel pro-apoptotic tumor suppressor that is lost during GIST tumorigenesis.

Targeting Disease Persistence in Gastrointestinal Stromal Tumors

“…We recently reported that in both imatinib-sensitive and imatinib-resistant GIST cells, and in tumorigenic ICC-SCs, reduced apoptosis sensitivity could also reflect loss of family with sequence similarity 96, member A (FAM96A) [59]. FAM96A is a member of the cytosolic ironsulfur protein assembly machinery and a regulator of cellular iron homeostasis [60], but we found its proapoptotic action to be dependent on its evolutionarily conserved ability to bind apoptotic peptidase activating factor 1 (APAF1).…”

A multi-target protein of hTERTR-FAM96A presents significant anticancer potent in the treatment of hepatocellular carcinoma

“…Furthermore, the results in Figure 1(e) and (f) demonstrate that hTERT and Apaf-1 expression levels were upregulated in HCC cells, which is consistent with previous studies. 17,19 These results indicate that the fusion protein hTERTR-FAM96A was successfully expressed and specifically bound with its target molecules of both hTERT and Apaf-1.…”

Gastrointestinal stromal tumors (GIST): Facing cell death between autophagy and apoptosis

“…a promising strategy to overcome imatinib resistance via apoptosis induction [ x e.g., AUY922, in phase II trial -NCT01389583]. [81]. FAM96A !…”

“…80 Recently, Schwamb and collaborators suggested a pro-apoptotic-tumor suppressor role for FAM96A, by interacting with APAF1. 81 The authors revealed that FAM96A protein expression is profoundly reduced or missing in 2 independent cohorts of GIST samples. GIST and autophagy signaling.…”

“…81 Interestingly, re-establishment of FAM96A expression in GIST cell lines increases tumor sensitivity to apoptosis. Thus, identifying novel pro-apoptotic molecules such as FAM96A and elucidating their mechanisms may represent an innovative tool to fully restore mitochondrial apoptosis in GIST patients.…”