FAVL elevation in human tumors disrupts Fanconi anemia pathway signaling and promotes genomic instability and tumor growth

Abstract

Fanconi anemia (FA) is a rare human genetic disease caused by mutations in any one of 13 known genes that encode proteins functioning in one common signaling pathway, the FA pathway, or in unknown genes. One characteristic of FA is an extremely high incidence of cancer, indicating the importance of the FA pathway in tumor suppression. However, the role of this pathway in the development and progression of human cancers in individuals who do not have FA has not been clearly determined. Here, we report that elevated expression of what we believe to be a novel splice variant of FA complementation group L (FANCL), which we identified and named FAVL, can impair the FA pathway in non-FA human tumor cells and act as a tumor promoting factor. FAVL expression was elevated in half of the human carcinoma cell lines and carcinoma tissue samples tested. Expression of FAVL resulted in decreased FANCL expression by sequestering FANCL to the cytoplasm and enhancing its degradation. Importantly, this impairment of the FA pathway by FAVL elevation provided human cancer cells with a growth advantage, caused chromosomal instability in vitro, and promoted tumor development in a xenograft mouse model. These data indicate that FAVL impairment of the FA pathway likely contributes to the development of non-FA human cancers and therefore add a challenging layer of complexity to the pathogenesis of human cancer. We further believe that these data will prove useful for developing additional tools for fighting human cancer.

Analysis of a FANCE Splice Isoform in Regard to DNA Repair

“…Indeed, splice variants seem to act as regulators of the FA pathway, as observed in the well-characterized FAVL variant. In that case, FAVL has been demonstrated to promote FANCL degradation42,77 . The expression of the splice isoform was increased in the presence of sequence variation rs77950394 and rs182189246, while rs13214239 reduces its expression.…”

“…Only a few FANCE-deficient patients were identified to date but most of them display several major abnormalities, thus demonstrating the importance of the integrity of the FANCE protein39,40 . Alternatively splice isoforms were previously analyzed and characterized for other FA genes namely FANCA, FANCC or FANCL35,[41][42][43] . This study represents the first characterization of a FANCE splice isoform lacking the exon 4 (designated FANCE∆4) and annotated in the NCBI database as XM_005248886.1.Co-immunoprecipitation and yeast-2-hybrid studies have already demonstrated the direct interaction of the FANCE protein with FANCC and FANCD2, thus suggesting that binding of FANCE∆4 with these partners could be altered32,44 .…”

“…As recently reported, a similar behavior was observed with FANCC∆7 and FANCL∆4 isoforms regarding FANCD2 monoubiquitination. Indeed, without activation of the FA pathway, ICL DNA repair cannot occur, which is in accordance with the increased G2/M cell accumulation and cell survival reduction we observed.It is recognized that alternative splicing can regulate protein translocation to the nucleus42,59 . The direct interaction with FANCC and the presence of NLSs in FANCE protein are crucial for its In this study, we have shown that FANCE∆4 and FANCE interact with each other.…”

Fanconi anaemia: from a monogenic disease to sporadic cancer

“…As discussed before, defects of the FA/BRCA pathway in cancer cells have also been related to the expression of FA variant proteins, such as the FAVL variant [41]. As is the case in conventional FA cells, cell lines expressing high levels of FAVL were hypersensitive to MMC, an observation with evident implications in the development of optimised cancer therapies with DNA ICL agents.…”

“…Strikingly, in their study, Zhang et al observed that FAVL was expressed in 50% of tested carcinoma cell lines and primary carcinomas, and that expression of FAVL mediated a decrease in FANCL expression. Moreover, FAVL provided cancer cells with a growth advantage, caused chromosomal instability and promoted tumour development in a xenograft mouse model [41].…”