MOF mediated acetylation attenuates SIRT6 tumor suppressive activity in non-small cell lung cancer

Abstract

SIRT6 (Silent information regulator protein 6 or Sirtuin 6) is a NAD+-dependent deacetylase, defatty-acylase and mono-ADP-ribosyl transferase with established roles in a spectrum of biological processes including DNA damage repair, genome maintenance, metabolic homeostasis, inflammatory response, stem cell homeostasis, aging and tumor suppression. Although intensive efforts have been made to decipher SIRT6-mediated downstream functions, only few studies have focused on elucidating the upstream regulation of SIRT6. Post-translational modification is an efficient and dynamic mechanism that cell used to modulate protein function in response to diverse cellular stimuli, and up to now, only limited works have revealed the post-translational modifications of SIRT6 and their functional relevance. In this work, a novel upstream regulatory mechanism of SIRT6 has been unveiled in which acetylation, a widely exist protein post-translational modification, can modulate SIRT6 deacetylase activity. I further identify MOF (Males absent on the first, also known as KAT8 or MYST1) is the major acetyltransferase responsible for SIRT6 acetylation, and HDAC1 or SIRT6 itself is the potential deacetylase of SIRT6. Using mass spectrometry, three evolutionary conserved lysine residues within the core catalytic domain of SIRT6 are identified as the main acetylation sites targeted by MOF. MOF mediated acetylation does not affect SIRT6 nuclear localization and protein stability, but significantly reduces SIRT6 deacetylase activity towards its histone substrates H3K9ac and H3K56ac both in vitro and in vivo.

Functionally, MOF mediated acetylation attenuates SIRT6 tumor suppressive activity in non-small cell lung cancer (NSCLC). Although expression of wildtype SIRT6 significantly suppresses the tumorigenic potential in NSCLC cells, expression of SIRT6 mutant mimicking a constitutive acetylation by MOF fails to repress cell proliferation, colony formation, and in vivo tumor growth. Interestingly, overexpression of MOF is sufficient to abolish the SIRT6 mediated tumor suppressive effect in NSCLC cells, indicating a direct regulatory effect towards SIRT6 by MOF. Mechanistically, ZEB2 is identified to be a SIRT6 target gene in NSCLC cells and SIRT6 directly regulates ZEB2 expression through deacetylating H3K9ac and H3K56ac at ZEB2 promoter region. Acetylation of SIRT6 fails to deacetylate these histone marks at ZEB2 promoter and de-represses ZEB2 expression thus promoting NSCLC. Taken together, this study provides novel insights into the upstream regulation of SIRT6 and uncovers a mechanism in which MOF mediated acetylation of SIRT6 promotes NSCLC progression. Therapeutically, the results present in this work may inspire the development of novel strategies to target SIRT6 acetylation to treat NSCLC.