Lohmann, E. | Search bioRxiv

bioRxiv2022

The E2F4/p130 repressor complex cooperates with oncogenic ΔNp73α to promote cell survival in human papillomavirus 38 E6/E7-transformed keratinocytes and in cancer cells

Tumor suppressor p53 and its related proteins, p63 and p73, can be synthesized as multiple isoforms lacking part of the N- or C-terminal regions. Specifically, high expression of the {Delta}Np73 isoform is notoriously associated with various human malignancies characterized by poor prognosis. This isoform is also accumulated by oncogenic viruses such as Epstein-Barr virus (EBV), as well as genus beta human papillomaviruses (HPV) that appear to be involved in carcinogenesis. To gain additional insight into {Delta}Np73 mechanisms, we have performed proteomics analyses using human keratinocytes transformed by the E6 and E7 proteins of the beta-HPV type 38 virus as an experimental model (38HK). We find that {Delta}Np73 associates with the E2F4/p130 repressor complex through a direct interaction with E2F4. This interaction is favored by the N-terminal truncation of p73 characteristic of {Delta}Np73 isoforms. Moreover, it is independent of the C-terminal splicing status, suggesting that it could represent a general feature of {Delta}Np73 isoforms (, {beta}, {gamma}, {delta}, {varepsilon}, {zeta}, {theta}, {eta}, and {eta}1). We also show that the {Delta}Np73- E2F4/p130 complex inhibits the expression of specific genes, including genes encoding for negative regulators of proliferation, both in 38HK and in HPV-negative cancer-derived cell lines. Consistently, silencing of E2F4 in 38HK and in cancer cells results in induction of senescence. In conclusion, we have identified and characterized a novel transcriptional regulatory complex that exerts pro-survival functions in transformed cells. IMPORTANCEThe TP53 gene is mutated in about 50% of human cancers. In contrast, the TP63 and TP73 genes are rarely mutated but rather expressed as {Delta}Np63 and {Delta}Np73 isoforms in a wide range of malignancies, where they act as p53 antagonists. Accumulation of {Delta}Np63 and {Delta}Np73, which is associated with chemoresistance, can result from infection by oncogenic viruses such as EBV or HPV. Our study focuses on the highly carcinogenic {Delta}Np73 isoform and uses a viral model of cellular transformation. We unveil a physical interaction between {Delta}Np73 and the E2F4/p130 complex involved in cell cycle control, which rewires the E2F4/p130 transcriptional program. Consistently, we find that E2F4 gains pro-survival functions in transformed cells expressing {Delta}Np73. This report shows, for the first time, that {Delta}Np73 isoforms acquire novel protein-protein interactions with respect to the TAp73 tumor suppressor. This situation is analogous to the gain-of-function interactions of p53 mutants supporting cellular proliferation.

cancer biology↗

bioRxiv2020

Bi-allelic variants in TSPOAP1, encoding the active zone protein RIMBP1, cause autosomal recessive dystonia

Dystonia is a debilitating hyperkinetic movement disorder, frequently transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense and missense variants in TSPOAP1, encoding the active zone RIM-binding protein 1 (RIMBP1), as a novel genetic cause of autosomal recessive dystonia in seven subjects from three unrelated families. Subjects carrying loss-of-function variants presented with juvenile- onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between presynaptic RIMBP1 dysfunction and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

genetics↗