Fanconi anemia deficiency stimulates HPV-associated hyperplastic growth in organotypic epithelial raft culture.

Fanconi anemia (FA) is a recessive genome instability syndrome characterized by heightened cellular sensitivity to DNA damage, aplastic anemia and cancer susceptibility. Leukemias and squamous cell carcinomas (SCCs) are the most predominant FA-associated cancers, with the latter exhibiting markedly early disease onset and aggressiveness. Although studies of hematopoietic cells derived from FA patients have provided much insight into bone marrow deficiencies and leukemogenesis, molecular transforming events in FA-deficient keratinocytes, which are the cell type of origin for SCC, are poorly understood. We describe here the growth and molecular properties of FANCA-deficient versus FANCA-corrected HPV E6/E7 immortalized keratinocytes in monolayer and organotypic epithelial raft culture. In response to DNA damage, FANCA-deficient patient-derived keratinocyte cultures displayed a G2/M phase arrest, senescence and apoptosis. Organotypic raft cultures exhibited DNA repair-associated defects with more 53BP1 foci and TdT-mediated dNTP nick end labeling-positive cells over their corrected counterparts. Interestingly, together with reduced rates of DNA damage, FA correction resulted in a marked decrease in epithelial thickness and the presence of fewer cell layers. The observed FANCA-mediated suppression of hyperplasia correlated with the detection of fewer cells transiting through the cell cycle in the absence of gross differentiation abnormalities or apoptotic differences. Importantly, the knockdown of either FANCA or FANCD2 in HPV-positive keratinocytes was sufficient for increasing epithelial hyperplasia. Our findings support a new role for FA pathways in the maintenance of differentiation-dependent cell cycle exit, with the implication that FA deficiencies may contribute to the high risk of FA patients for developing HPV-associated SCC.

Coordinate regulation of Fanconi anemia gene expression occurs through the Rb/E2F pathway.

Fanconi anemia (FA) is a genome instability syndrome that is characterized by progressive bone marrow failure and a high risk of cancer. FA patients are particularly susceptible to leukemia as well as squamous cell carcinomas (SCCs) of the head and neck, anogenital region and skin. Thirteen complementation groups and the corresponding FA genes have been identified, and their protein products assemble into nuclear core complexes during DNA-damage responses. Much progress has been made in our understanding of post-translational FA protein modifications and physical interactions. By contrast, little is known about the control of protein availability at the level of transcription. We report here that multiple FA proteins were downregulated during the proliferative arrest of primary human keratinocytes and HeLa cells, and that the observed regulation was at a transcriptional level. Proliferative stimuli such as expression of HPV16 E7 as well as E2F1 overexpression in primary cells resulted in coordinate FA upregulation. To define the underlying mechanism, we examined the endogenous FANCD2 promoter, and detected regulated binding of members of the E2F/Rb family in chromatin immunoprecipitation assays. Finally, a 1 kb promoter fragment was sufficient to confer E2F/Rb regulation in reporter assays. Taken together, our data demonstrate FA gene co-regulation in synchrony with the cell cycle and suggest that deregulated expression of individual FA genes-in addition to FA gene mutation-may promote FA-related human cancer.