# Characterizing the tumor suppressor activity of FLCN in Birt-Hogg-Dubé syndrome through transcriptiomic and proteomic analysis

## TL;DR

This study explores how the loss of the FLCN gene contributes to cancer in Birt-Hogg-Dubé syndrome by affecting cell cycle control and DNA damage response.

## Contribution

The study reveals a novel interaction between FLCN and DNA-PK, linking FLCN to DNA damage response and cell cycle regulation.

## Key findings

- FLCN knockdown in HK2 cells increases tumorigenic potential and alters cell cycle gene expression.
- FLCN interacts with DNA-PK, and this interaction is reversed by irradiation.
- Defective cell cycle arrest in Flcn-knockdown C. elegans supports FLCN's role in DNA damage response.

## Abstract

Birt-Hogg-Dubé (BHD) syndrome patients are uniquely susceptible to all renal tumour subtypes. The underlying mechanism of carcinogenesis is unclear. To study cancer development in BHD, we used human proximal kidney (HK2) cells and found that long-term folliculin (FLCN) knockdown was required to increase their tumorigenic potential, forming larger spheroids in non-adherent conditions. Transcriptomic and proteomic analysis uncovered links between FLCN, cell cycle control and the DNA damage response (DDR) machinery. HK2 cells lacking FLCN had an altered transcriptome profile with cell cycle control gene enrichment. G1/S cell cycle checkpoint signaling was compromised with heightened protein levels of cyclin D1 (CCND1) and hyperphosphorylation of retinoblastoma 1 (RB1). A FLCN interactome screen uncovered FLCN binding to DNA-dependent protein kinase (DNA-PK). This novel interaction was reversed in an irradiation-responsive manner. Knockdown of FLCN in HK2 cells caused a marked elevation of γH2AX and RB1 phosphorylation. Both CCND1 and RB1 phosphorylation remained raised during DNA damage, showing an association with defective cell cycle control with FLCN knockdown. Furthermore, Flcn-knockdown C. elegans were defective in cell cycle arrest by DNA damage. This work implicates that long-term FLCN loss and associated cell cycle defects in BHD patients could contribute to their increased risk of cancer.