Biology subjects

Chelakkot, V. S.

Publications and source records attributed to Chelakkot, V. S..

2 recordsLinked to original sources

bioRxiv2025

XPC loss-of-function triggers melanomagenesis through CDKN2A downregulation

We identified a novel XPC variant, c.2420+5G>A (XPCvar), in siblings with multiple melanomas, inherited alongside c.779+1G>T, which results in an absent or disrupted protein. However, they did not exhibit significantly higher nucleotide excision repair (NER) deficits compared to their unaffected parents, suggesting an NER-independent tumor suppressor function for XPC. XPC knockdown increased cell proliferation and tumorigenicity in vitro without affecting NER. Single-cell RNA sequencing revealed lower Cdkn2a in Xpcvar/var mouse melanocytes. Additionally, XPC knockdown downregulated CDKN2A in vitro. Furthermore, patient fibroblasts showed decreased p16INK4a, which was rescued by XPC overexpression. ChIP-PCR and luciferase assays confirmed XPC binding to the CDKN2A promoter, initiating transcription. Premature stop codon read-through, with gentamicin, restored XPC and p16INK4A in patient fibroblasts. These suggest that XPC regulates CDKN2A and XPC loss might promote melanomagenesis by downregulating CDKN2A, independent of its NER function. We provide preclinical evidence for potential preventive and/or therapeutic strategies for similarly affected individuals. STATEMENT OF SIGNIFICANCECharacterizing a novel XPC variant identified in patients with melanoma revealed a non-canonical role for XPC in regulating CDKN2A transcription. XPC binding to the CDKN2A promoter is crucial for CDKN2A expression and might suppress melanomagenesis. This expands our understanding of melanomagenesis and suggests potential therapies targeting XPC-mediated regulation of CDKN2A.

cancer biology↗

bioRxiv2020

MEK reduces cancer-specific PpIX accumulation through the RSK-ABCB1 and HIF-1α-FECH axes

The efficacy of aminolevulinic acid (5-ALA)-based photodynamic diagnosis (5-ALA-PDD) and photodynamic therapy (5-ALA-PDT) is dependent on the 5-ALA-induced cancer-specific accumulation of protoporphyrin IX (PpIX). We previously reported that inhibition of oncogenic Ras/MEK increases PpIX accumulation in cancer cells by reducing PpIX efflux through ATP-binding cassette sub-family B member 1 (ABCB1) as well as PpIX conversion to heme by ferrochelatase (FECH). Here, we sought to identify the downstream pathways of Ras/MEK involved in the regulation of PpIX accumulation via ABCB1 and FECH. First, we demonstrated that Ras/MEK activation reduced PpIX accumulation in RasV12-transformed NIH3T3 cells and HRAS transgenic mice. Knockdown of p90 ribosomal S6 kinases (RSK) 2, 3, or 4 increased PpIX accumulation in the RasV12-transformed NIH3T3 cells. Further, treatment with an RSK inhibitor reduced ABCB1 expression and increased PpIX accumulation. Moreover, HIF-1 expression was reduced when the RasV12-transformed NIH3T3 cells were treated with a MEK inhibitor, demonstrating that HIF-1 is a downstream element of MEK. HIF-1 inhibition decreased the activity of FECH and increased PpIX accumulation. Finally, we demonstrated the involvement of RSKs and HIF-1 in the regulation of PpIX accumulation in human cancer cell lines (DLD-1, SNB-75, Hs 578T, and MDA MB 231). These results demonstrate that the RSK-ABCB1 and HIF-1-FECH axes are the downstream pathways of Ras/MEK involved in the regulation of PpIX accumulation.

cancer biology↗