Age and insulin-like growth factor-1 impact PCNA monoubiquitination in UVB-irradiated human skin

Rebekah J Hutcherson,Ryan D Gabbard,Amber J Castellanos,Jeffrey B Travers,Michael G Kemp

doi:10.1016/j.jbc.2021.100570

Abstract

Nonmelanoma skin cancers occur primarily in individuals over the age of 60 and are characterized by an abundance of ultraviolet (UV) signature mutations in keratinocyte DNA. Though geriatric skin removes UV photoproducts from DNA less efficiently than young adult skin, it is not known whether the utilization of other prosurvival but potentially mutagenic DNA damage tolerance systems such as translesion synthesis (TLS) is altered in older individuals. Using monoubiquitination of the replicative DNA polymerase clamp protein PCNA (proliferating cell nuclear antigen) as a biochemical marker of TLS pathway activation, we find that UVB exposure of the skin of individuals over the age of 65 results in a higher level of PCNA monoubiquitination than in the skin of young adults. Furthermore, based on previous reports showing a role for deficient insulin-like growth factor-1 (IGF-1) signaling in altered UVB DNA damage responses in geriatric human skin, we find that both pharmacological inhibition of the IGF-1 receptor (IGF-1R) and deprivation of IGF-1 potentiate UVB-induced PCNA monoubiquitination in both human skin ex vivo and keratinocytes in vitro. Interestingly, though the TLS DNA polymerase Pol eta can accurately replicate the major photoproducts induced in DNA by UV radiation, we find that it fails to accumulate on chromatin in the absence of IGF-1R signaling and that this phenotype is correlated with increased mutagenesis in keratinocytes in vitro. Thus, altered IGF-1/IGF-1R signaling in geriatric skin may predispose epidermal keratinocytes to carry out a more mutagenic form of DNA synthesis following UVB exposure.

Highlights

Young adults [4,5,6,7], which indicates that impaired excision repair may contribute to mutagenesis and carcinogenesis in older individuals
Age and insulin-like growth factor-1 (IGF-1) impact proliferating cell nuclear antigen (PCNA) monoubiquitination in human skin specific translesion synthesis (TLS) polymerases are recruited to UV lesions in DNA, the monoubiquitination of the replicative polymerase clamp protein PCNA is generally considered to be a key signal involved in the recruitment of TLS polymerases to sites of damage because these enzymes contain ubiquitinbinding domains [15, 17]
We showed for the first time that PCNA monoubiquitination, a posttranslational modification associated with the activation of the TLS pathway and the recruitment of specialized DNA polymerases to sites of DNA damage [15, 17], can be readily detected in human skin epidermis following UVB exposure (Fig. 1)

Summary

Introduction

Young adults [4,5,6,7], which indicates that impaired excision repair may contribute to mutagenesis and carcinogenesis in older individuals. We show that an antibody against the monoubiquitinated form of PCNA can be used to readily detect this important biochemical marker of TLS in UVB-irradiated human skin. The loss of IGF-1 receptor signaling potentiates UVB-induced PCNA monoubiquitination in cultured keratinocytes in vitro

Results

Conclusion