Original article
Metastasis suppressor proteins in cutaneous squamous cell carcinoma

https://doi.org/10.1016/j.prp.2015.12.018Get rights and content

Abstract

Cutaneous squamous cell carcinomas (cSCCs) are common human carcinomas. Despite having metastasizing capacities, they usually show less aggressive progression compared to squamous cell carcinoma (SCC) of other organs. Metastasis suppressor proteins (MSPs) are a group of proteins that control and slow-down the metastatic process. In this study, we established the importance of seven well-defined MSPs including NDRG1, NM23-H1, RhoGDI2, E-cadherin, CD82/KAI1, MKK4, and AKAP12 in cSCCs.

Protein expression levels of the selected MSPs were detected in 32 cSCCs, 6 in situ SCCs, and two skin cell lines (HaCaT, A-431) by immunohistochemistry. The results were evaluated semi-quantitatively using the HSCORE system. In addition, mRNA expression levels were detected by qRT-PCR in the cell lines.

The HSCOREs of NM23-H1 were similar in cSCCs and normal skin tissues, while RGHOGDI2, E-cadherin and AKAP12 were significantly downregulated in cSCCs compared to normal skin. The levels of MKK4, NDRG1 and CD82 were partially conserved in cSCCs. In stage I SCCs, nuclear staining of NM23-H1 (NM23-H1nuc) was significantly lower than in stage II/III SCCs. Only nuclear staining of MKK4 (MKK4nuc) showed significantly higher scores in in situ carcinomas compared to invasive SCCs.

In conclusion, similar to other human tumors, we have demonstrated complex differential expression patterns for the MSPs in in-situ and invasive cSCCs. This complex MSP signature warrants further biological and experimental pathway research.

Introduction

Non-melanoma skin cancers (NMSC) are the most common human malignant neoplasms, and create significant medical, economical, and social problems for the healthcare services worldwide [1], [2], [3]. Although there are other types of NMSC, this term commonly refers to the two common neoplasms of cutaneous squamous cell carcinoma (cSCC) and basal cell carcinoma (BCC) [1]. BCCs are slow growing, malignant, yet rarely metastasizing carcinomas [4]. On the contrary, cSCCs are more aggressive in behavior, and have considerably higher metastatic capacities than BCCs [4].

Metastasis is a very complex and multistep biological process directed by various proteins and pathways [5]. Though various proteins support metastasis, a group of proteins called metastasis suppressor proteins (MSPs) specifically inhibit or slow metastasis [6], [7]. As a definition, pure MSPs should only suppress metastasis without any effect on tumorigenicity (e.g. proliferation). However, in the complex environment of a cell, they usually have other important properties as tumor suppressor activities, affecting carcinogenesis, besides these MSP functions [6]. cSCCs differ from internal identical organ cancers in that they have lower metastatic rates and result in better prognosis [4]. Thus, cSCCs are interesting biological models for the research of metastasis suppressors. To establish the importance of the MSPs in non-melanoma skin cancer, we selected seven essential and well-defined MSPs (NDRG1, NM23-H1, RhoGDI2, E-cadherin, CD82/KAI1, MKK4, and AKAP12) that affect different steps of metastasis.

The main aim of this study was to analyze the expression patterns of these seven important MSPs that may contribute to the inhibition of metastasis pathways in cSCCs, as well as in squamous cell lines. We also established the association between these proteins and important clinicopathological parameters in cSCC.

Section snippets

Study groups

A total of 38 SCCs composed of 32 tissue samples of classical squamous cell carcinoma (SCC-NOS) of the skin and 6 in situ carcinoma tissues, obtained from 37 patients (26M/11F), were included in this study. All patients were Caucasians, and the detailed characteristics of the study group are summarized in Appendix 1. SCCs were graded by four-tiered system as well (Grade 1), moderately (Grade 2) poorly differentiated (Grade 3) and anaplastic or undifferentiated tumors (Grade 4) [8]. Data for the

Tissue study

Cytoplasmic positivity of NM23-H1 (NM23-H1cyt) and NDRG1 (NDRG1cyt) was detected to be strong and homogeneous in all of the in situ and invasive cSCCs (Fig. 1A, B, F, G). However, nuclear NM23-H1 (NM23-H1nuc) expression was significantly weaker and was detected in only two of in situ SCCs (IS-SCC, 33.3%) and 15 cSCCs (46.8%) compared to normal skin. Nuclear positivity of NDRG1 (NDRG1nuc) was seen in 4 of 6 IS-SCCs (66.6%), and 29 of 32 cSCCs (90.6%).

E-cadherin, CD82 and AKAP12 proteins show

Discussion

In this study, we demonstrated different expression patterns of MSPs in cutaneous SCCs. NM23-H1 levels were conserved in in situ and invasive carcinomas, and in squamous carcinoma cell lines. Although the role of NM23-H1 in metastasis suppression is well described in other carcinomas, it is not clear in NMSC [6], [7]. Similar to our findings, Ro et al. [14] and Stephenson et al. [15] showed that the expression of NM23-H1 was well conserved in cSCCs of the skin and keratoacanthomas (KA).

Conclusions

Although NM23-H1 expression was maintained at constant levels, RGHOGDI2, E-cadherin, and AKAP12 were significantly downregulated in cSCCs. Furthermore, MKK4, NDRG1 and CD82 were also partially expressed in cSCCs. Similar to other human tumors, cSCCs show a distinct MSP profile. Data from this study might also reveal possible pathways among MSPs, when combined with the current knowledge on related pathways. This relationship between these MSPs warrants further biological and experimental pathway

Acknowledgements

This study was financially supported by the Scientific and Technical Research Council of Turkey (TUBITAK, grant number SBAG-108S184). The project was approved by the Kırıkkale University Local Ethics Committee (07.04.2008/2008-039).

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