A Hidden Role of the Inactivated FANCD2: Upregulating ΔNp63

Jayabal Panneerselvam,Junnian Zheng,Peiwen Fei,Hui Tian,Jun Zhang,Hong Wang,Anna Pickering

doi:10.18632/oncotarget.1217

Abstract

A compromised Fanconi Anemia (FA) signaling pathway, often resulting from an inactivated FANCD2, was recently recognized to contribute to the development of non-FA human tumors. However, it is largely unknown as to how an impaired FA pathway or an inactivated FANCD2 promotes tumorigenesis. Here we unexpectedly found that ΔNp63 mRNA was expressed at high levels in human cancer cells carrying an impaired FA pathway compared to the corresponding control cells carrying an intact FA pathway. This observation was recapitulated upon conditionally managing the status of FANCD2 monoubiquitination /activation in 293T cells. Importantly, ΔNp63 elevation upon FANCD2 inactivation was confirmed in human fibroblasts derived from FA patients. Moreover, we have identified a 189 bp DNA fragment downstream of the ΔNp63 promoter (P2) that can mediate the upregulation of ΔNp63 by an inactivated FANCD2, and determined that elevated ΔNp63 is high enough to promote cancer cell proliferation and metastasis. In vivo, the elevation of FAVL, a tumor promotion factor that inhibits FANCD2 activation, was found to be positively associated with ΔNp63 expression in human cancer tissues. Collectively, these results document a novel role of an inactivated FANCD2 in upregulating ΔNp63, advancing our understanding of how an impaired FA pathway contributes to the pathogenesis of human cancer.

Highlights

The alternative promoter (P2) of p63 leads to deleted-transactivation domain (TA) isoforms (ΔNp63), while transcription starting at the P1 promoter of p63 produces TA-containing p63 isoforms [1,2,3,4]
To confirm that ΔNp63 elevation results from an inactivated FANCD2, not from the offtarget effect of FANCL silencing, we detected ΔNp63 expression in stably-transfected cell pairs derived from the HTB-4 bladder cancer cell line, in which the impaired Fanconi Anemia (FA) pathway was induced by a high expression level of FAVL [17, 18]
This suggests that the regulation of ΔNp63 expression by inactivated FANCD2 may play an important role in the development of human tumors, presumably starting from tumor initiation to tumor mass development, which often leads to hypoxic conditions within solid tumors

Summary

Introduction

The alternative promoter (P2) of p63 leads to deleted-transactivation domain (TA) isoforms (ΔNp63), while transcription starting at the P1 promoter of p63 produces TA-containing p63 isoforms [1,2,3,4]. P63containing the transactivation domain is capable of inducing apoptosis and inhibiting cell-cycle progression, suppressing tumor development [1,2,3, 5,6,7]. The ΔNp63 variants are often overexpressed in a variety of human cancers, including squamous cell origin (head and neck, lung), breast and bladder [8]. The improper function / transduction of the FA pathway confers the defects in repairing damaged DNA, especially DNA crosslinks, and leads to chromosome instability and the development of both FA and non-FA human tumors [15, 17,18,19,20]. FANCD2 monoubiquitination is a hallmark of the activation of the FA pathway, and un-monoubiquitinated www.impactjournals.com/oncotarget

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