Cyld Inhibits Tumor Cell Proliferation by Blocking Bcl-3-Dependent NF-κB Signaling

Abstract

Mutations in the CYLD gene cause tumors of hair-follicle keratinocytes. The CYLD gene encodes a deubiquitinase that removes lysine 63-linked ubiquitin chains from TRAF2 and inhibits p65/p50 NF-kappaB activation. Here we show that mice lacking Cyld are highly susceptible to chemically induced skin tumors. Cyld-/- tumors and keratinocytes treated with 12-O-tetradecanoylphorbol-13 acetate (TPA) or UV light are hyperproliferative and have elevated cyclin D1 levels. The cyclin D1 elevation is caused not by increased p65/p50 action but rather by increased nuclear activity of Bcl-3-associated NF-kappaB p50 and p52. In Cyld+/+ keratinocytes, TPA or UV light triggers the translocation of Cyld from the cytoplasm to the perinuclear region, where Cyld binds and deubiquitinates Bcl-3, thereby preventing nuclear accumulation of Bcl-3 and p50/Bcl-3- or p52/Bcl-3-dependent proliferation. These data indicate that, depending on the external signals, Cyld can negatively regulate different NF-kappaB pathways; inactivation of TRAF2 controls survival and inflammation, while inhibition of Bcl-3 controls proliferation and tumor growth.

An inactivating CYLD mutation promotes skin tumor progression by conferring enhanced proliferative, survival and angiogenic properties to epidermal cancer cells

“…Our results show an important increase in the total amount of both proteins (Figure 1b) and their preferential nuclear localization in the C57-CYLD C/S cells (Figure 3g). The increase in nuclear Bcl3 and b-catenin expression was accompanied by an increase in nuclear p52 in the mutant cells as it has been previously reported (Massoumi et al, 2006). …”

“…Increased nuclear localization of p50/p52 and Bcl3 was also found in advanced stages of mouse skin carcinomas (Budunova et al, 1999). Nuclear Bcl3 has been detected in cylindroma cells, whereas normal skin keratinocytes retain Bcl3 in the cytoplasm (Massoumi et al, 2006). An increase in nuclear Bcl3 accumulation and transcription of cyclin D1 was also observed in CYLD-deficient keratinocytes (Massoumi et al, 2006).…”

“…This mutant carries the 601 C/S point mutation in the cysteine box of the deubiquitinase domain, resulting in a catalitically inactive protein that is able to compete with the endogenous CYLD (Brummelkamp et al, 2003;Trompouki et al, 2003;Massoumi et al, 2006Massoumi et al, , 2009. The PDVC57 cells were chosen because they bear a Ha-ras mutation carried by all the chemically induced mouse skin tumors and some human skin carcinomas (Pierceall et al, 1991;Spencer et al, 1995).…”

“…Thus, mice deficient in CYLD are more susceptible to develop chemically induced skin tumors (Massoumi et al, 2006;Massoumi and Paus, 2007). In this case, the loss of CYLD in keratinocytes was linked to hyperproliferation and elevation in cyclin D1 levels because of increased nuclear activity of Bcl-3-associated NF-kB p50 and p52 and is independent of the classical p65/NF-kB pathway (Massoumi et al, 2006).…”

“…Thus, mice deficient in CYLD are more susceptible to develop chemically induced skin tumors (Massoumi et al, 2006;Massoumi and Paus, 2007). In this case, the loss of CYLD in keratinocytes was linked to hyperproliferation and elevation in cyclin D1 levels because of increased nuclear activity of Bcl-3-associated NF-kB p50 and p52 and is independent of the classical p65/NF-kB pathway (Massoumi et al, 2006). These investigators reported that in the case of non-melanoma skin cancer (NMSC) the analysis by microarrays of different types of human tumors suggests that there is a relationship between the level of CYLD expression and the grade of malignancy of the tumor: CYLD is clearly detected in normal skin, less expressed in benign basal cell carcinomas and poorly detected in malignant squamous cell carcinomas (SCCs) (Massoumi et al, 2006).…”