CYLD regulates keratinocyte differentiation and skin cancer progression in humans

Abstract

CYLD is a gene mutated in familial cylindromatosis and related diseases, leading to the development of skin appendages tumors. Although the deubiquitinase CYLD is a skin tumor suppressor, its role in skin physiology is unknown. Using skin organotypic cultures as experimental model to mimic human skin, we have found that CYLD acts as a regulator of epidermal differentiation in humans through the JNK signaling pathway. We have determined the requirement of CYLD for the maintenance of epidermal polarity, keratinocyte differentiation and apoptosis. We show that CYLD overexpression increases keratinocyte differentiation while CYLD loss of function impairs epidermal differentiation. In addition, we describe the important role of CYLD in the control of human non-melanoma skin cancer progression. Our results show the reversion of the malignancy of human squamous cell carcinomas that express increased levels of CYLD, while its functional inhibition enhances the aggressiveness of these tumors which progress toward spindle cell carcinomas. We have found that the mechanisms through which CYLD regulates skin cancer progression include the control of tumor differentiation, angiogenesis and cell survival. These findings of the role of CYLD in human skin cancer prognosis make our results relevant from a therapeutic point of view, and open new avenues for exploring novel cancer therapies.

Functional Inactivation of CYLD Promotes the Metastatic Potential of Tumor Epidermal Cells

“…We have analyzed by smooth muscle actin immunostaining the pattern of blood vessels in both C57-Control-metastasis and CYLD C/S -metastasis and found that C57-CYLD C/S -metastases were highly vascularized (Figure 3h), whereas we hardly detected smooth muscle actinpositive staining in the C57-Control-metastasis (Figure 3g). This result is in agreement with our previous finding showing an enhanced angiogenesis in the skin tumors obtained by subcutaneous inoculation of both the murine C57 and human A431 SCC cells expressing the CYLD C/S mutant (Alameda et al, 2010(Alameda et al, , 2011a.…”

“…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. We found that the expression of the CYLD C/S mutant makes the squamous cancer PDVC57 cells (SCC cells) very aggressive, conferring them properties such as capacity of growing in suspension and increased angiogenesis that finally leads to a rapid tumor development in carcinogenesis assays (Alameda et al, 2010(Alameda et al, , 2011a. Now we have performed in vivo metastasis assays to ascertain whether CYLD has a role in the metastatic behavior of SCC epidermal cells.…”

“…We have recently reported on the role of CYLD in the homeostasis of the skin: it develops an important function in the maintenance of epidermal polarity, keratinocyte differentiation, and apoptosis (Alameda et al, 2011a).…”

“…SCCs account for B20% of all cutaneous malignancies, and may be very aggressive and invasive (Moller et al, 1979). Among the factors considered to play a role as SCC promoters, we have recently shown that the diminished function of CYLD in tumor epidermal cells worsens the prognosis of malignant skin tumors through enhancement of the expression of angiogenic factors and increase in the nuclear localization of Bcl3, p52, and b-catenin (Alameda et al, 2010(Alameda et al, , 2011a. In addition, we have shown that wild-type CYLD overexpression in human SCC cells reverts the malignant phenotype of the tumors (Alameda et al, 2011a).…”

“…Among the factors considered to play a role as SCC promoters, we have recently shown that the diminished function of CYLD in tumor epidermal cells worsens the prognosis of malignant skin tumors through enhancement of the expression of angiogenic factors and increase in the nuclear localization of Bcl3, p52, and b-catenin (Alameda et al, 2010(Alameda et al, , 2011a. In addition, we have shown that wild-type CYLD overexpression in human SCC cells reverts the malignant phenotype of the tumors (Alameda et al, 2011a). It has also been reported that mice lacking Cyld are highly susceptible to development of chemically induced benign skin tumors (Massoumi et al, 2006), and transgenic mice expressing a catalytically inactive mutant CYLD develop tumors of increased malignancy relative to nontransgenic mice (De Marval et al, 2011).…”