A role for Keratin 17 in Rac1-mediated DNA damage response in keratinocytes

Keratin 17 (K17) is a stress-responsive intermediate filament protein that is upregulated in chronic skin diseases and in several carcinomas. We previously showed that K17 is induced in epidermal keratinocytes following exposure to DNA damaging agents, promoting keratinocyte survival and chemically-induced papilloma formation in mouse skin. Molecularly, K17 is recruited to the nucleus where it impacts nuclear architecture, gene expression, and the DNA damage response (DDR). Here, we report on efforts to delineate K17-dependent processes during DDR by focusing on its interacting partners. Using mass spectrometry, we identified a network of K17-interacting Rho GTPase signaling proteins, including Rac1 and its activator Dock7. Biochemically, we confirmed that Rac1 and K17 interact directly in vitro and in A431 tumor keratinocytes, both at baseline and after ionizing radiation. We show that KRT17 deletion leads to decreased levels of Rac1 protein, its DNA damage-related effector TOP2A, and Rac1-dependent decrease in cellular proliferation following ionizing radiation. Remarkably, key K17-dependent readouts are rescued by expression of constitutively-active, but not dominant-negative, Rac mutants in KRT17 null A431 keratinocytes. These findings uncover a K17-Rac1-TOP2A signaling axis that promotes DNA damage response and associated proliferation, with implications for cancer and chronic skin diseases.