Identification of an AAA ATPase VPS4B-Dependent Pathway That Modulates Epidermal Growth Factor Receptor Abundance and Signaling during Hypoxia

Abstract

e VPS4B, an AAA ATPase (ATPase associated with various cellular activities), participates in vesicular trafficking and autophagosome maturation in mammalian cells. In solid tumors, hypoxia is a common feature and an indicator of poor treatment outcome. Our studies demonstrate that exogenous or endogenous (assessed with anchorage-independent three-dimensional multicellular spheroid culture) hypoxia induces VPS4B downregulation by the ubiquitin-proteasome system. Inhibition of VPS4B function by short hairpin VPS4B (sh-VPS4B) or expression of dominant negative VPS4B(E235Q) promotes anchorageindependent breast cancer cell growth and resistance to gefitinib, U0126, and genotoxicity. Biochemically, hyperactivation of epidermal growth factor receptor (EGFR), a receptor tyrosine kinase essential for cell proliferation and survival, accompanied by increased EGFR accumulation and altered intracellular compartmentalization, is observed in cells with compromised VPS4B. Furthermore, enhanced FOS/JUN induction and AP-1 promoter activation are noted in EGF-treated cells with VPS4B knockdown. However, VPS4B depletion does not affect EGFRvIII stability or its associated signaling. An inverse correlation between VPS4B expression and EGFR abundance is observed in breast tumors, and high-grade or recurrent breast carcinomas exhibit lower VPS4B expression. Together, our findings highlight a potentially critical role of VPS4B downregulation or chronichypoxia-induced VPS4B degradation in promoting tumor progression, unveiling a nongenomic mechanism for EGFR overproduction in human breast cancer.

The TIP60 Complex Is a Conserved Coactivator of HIF1A

“…Finally, to examine the roles of TIP60 and CDK8 in oncogenic properties of colorectal cancer cells, we measured the ability of shNT control, shTIP60, shCDK8, and HIF1A−/− HCT116 cells to initiate and sustain growth of three-dimensional colonies in soft agar, which quickly reach a size large enough to create hypoxic conditions at their core (Indovina et al, 2007; Lin et al, 2012; Meng et al, 2012; Sutherland et al, 1986). These assays are considered a good surrogate of the ‘tumor initiating ability’ of cancer cells (i.e.…”

A splicing mutation inVPS4Bcauses dentin dysplasia I

“…The cell cycle of the mutant gingival fibroblasts was changed with a marked decrease in G2/M phase, which might inhibit the proliferation of odontoblasts and thus affect dentin development (see online supplementary figure S4). Another finding is that VPS4B can act as a putative tumour suppressor to regulate the progression of cancer,32 33 and is also involved in degenerative diseases of the central nervous system 34. Undoubtedly, VPS4B as an AAA ATPase family member is a multifunctional protein, expression of which has also been detected in almost all human tissues in our study, but mutations in VPS4B are mainly associated with tooth anomalies in our index case, presumably because other proteins might compensate for the function of VPS4B in other tissues.…”

Effects of Membrane Trafficking on Signaling by Receptor Tyrosine Kinases

“…This is owing to the inhibition of Rab5-dependent fusion of early endosomes, resulting from the hypoxia-induced transcriptional down-regulation of Rab5 effector Rabaptin-5. Moreover, the levels of Vps4B ATPase that regulate endosomal trafficking are down-regulated on hypoxia, which leads to the accumulation of EGFR and its increased signaling (Lin et al 2012). Similarly, loss of VHL impairs internalization of fibroblast growth factor receptor 1 (FGFR1), causing its accumulation on the cell surface and enhanced signaling leading to increased cell motility on FGF stimulation (Hsu et al 2006;Champion et al 2008).…”