Introduction
Cutaneous squamous cell carcinoma (CSCC) is one of the most common cutaneous carcinoma in the elderly. With the extension of life expectancy in human, the prevalence of CSCC keeps rasing, with an annual global incidence more than 1 million [
1]. CSCC in situ is also known as Bowen’s disease (BD). If left untreated, BD may progress to invasive CSCC with the incidence of 3% ~ 5% [
2]. Photodynamic therapy is an alternative to surgery for BD. However, a retrospective study demonstrated that the 16 patients with BD who developed one or more CSCC after Photodynamic therapy treatment [
3]. The exact mechanisms by which BD progresses to CSCC are complicated and merits more attention. In addition, the patients with CSCC easy to occur metastasis and with a poor prognosis. Genders RE et al. [
4] published an excellent study regarding approximately 90% of CSCC metastases appear within 2 years after the initial diagnosis.
The proteomics technology has been successfully used to identify DEPs/DEGs in tumor tissues and to provide insights into the molecular mechanisms underlying and/or potential therapy targets for these complicated diseases [
5]. The proteomics changes in tumor tissues can directly and veritably reflect the local tumor microenvironment, thus providing a way to investigate the molecular mechanisms of tumor. Formalin-fixed paraffin-embedded (FFPE) tissue blocks represent a valuable source of samples for clinical research, as pathology departments routinely archive them in vast numbers. According to previous studies reported that FFPE tissues could provides opportunity for retrospective mass spectrometry-based (MS) proteomic profiling [
6,
7]. Bowen disease, also called cutaneous squamous cell carcinoma in situ, has been described as a premalignant intraepidermal lesion of the skin. Better understanding of aggressive growth and/or metastatic mechanisms of CSCC is urgent. Therefore, in this study, we applied this proteomics method to explore the proteomics change between CSCC, Bowen disease and healthy skin tissues. And next, we aim to explore some significant target proteins associated with CSCC and further verification by Western blot method.
Discussions
CSCC, a keratinocyte-derived skin neoplasm with malignant potential, represents 20–50% of skin cancers and currently has an increasing incidence in the world [
1]. The outcome of patients with CSCC mainly influenced by the TNM staging system, and the locally advanced, metastatic CSCC usually had poor outcomes. In recent years, the significantly progress has been made in the investigate the etiology of CSCC [
25]. In spite of such advances, CSCC is often discovered at an advanced stage and the exact mechanisms of invasion, metastasis and or therapeutic targets are greatly needed. Proteins have a considerable number of biological functions within the human body. The quantitative proteomics analysis of FFPE samples technologies are sensitive and provide greater coverage of the tissue proteomes of many complicated diseases, especially in tumors [
7,
26,
27]. Therefore, we compared the tumor samples proteomics change between CSCC (TNM staging: pT2 pN1 Mx, pT2 pN1 M1, pT1 pNx M1, pT3 pN1 M0 and pT3 pN1 Mx) and Bowen disease (primary CSCC), and to investigate the target proteins associated with mechanisms of invasion, metastasis in CSCC progress. In this proteomics study, we found that a numerous protein expression levels were significantly changed in the lesions between CSCC and Bowen disease. A total of 252 proteins were up-regulated and 104 proteins were down-regulated in the CSCC relative to the Bowen disease with a 1.5-fold change cut-off. Therefore, these significantly DEPs may play essential roles in the pathogenesis of malignant biological behaviors in CSCC. Bioinformatics tools were used to analyze the tumor biological behaviors and disease pathways which DEPs invloved. For example, our proteomics results indicated that the immune related inflammation (granulocyte activation, neutrophil mediated immunity, neutrophil activation, et al.), cell adhesion and tissue integrity (tight junction), devour process (endocytosis and Fc gamma R-mediated phagocytosis, et al
.) from the results of Figs.
4,
5. Theses biological process were mainly associated with the pathogenesis of invasion, metastasis mechanisms in CSCC. On the other hand, a total of 501 proteins were differentially expressed between the CSCC and healthy control, with 332 up-regulated and 169 down-regulated. To verify the these DEPs/DEGs accurateness and relevance, we further compared our proteomics data with the transcriptomic data for 13 samples with CSCC and paired 13 normal skin tissues [
28]. In two datasets, the expression levels of 20 common proteins trended in the same directions as in the RNA sequencing (RNA-seq) results (Fig.
7). Therefore, this 20 DEPs/DEGs were discerned to play an important role in the etiology of CSCC. And next, among 20 proteins, 8 proteins (TNC, FSCN1, SERPINB1, ACTN1, RAB31, COL3A1, COL1A1 and CD36) expressed levels showed significant differences between CSCC and Bowen disease.
The extensive family of COL gene products (collagens) is composed of several chain types, including fibril-forming interstitial collagens (types I, II, III and V) and basement membrane collagens (type IV), each type containing multiple isoforms. COL3A1 as well as COL1A1 play a role in cell adhesion process, important for maintaining normal tissue architecture and function [
29]. We found the proteins expressed levels of COL3A1 and COL1A1 were significant decreased in CSCC relative to Bowen disease according to Western blot results. This results indicated the higher-regulation of COL3A1 and COL1A1 could suppressed CSCC progression, which may be involved in the etiology of altered cell adhesion process. Whereas, in contrast to CSCC, the higher expression of COL1A1 could promote lung cancer [
12] and mesothelioma [
13] progression via immune infiltration mechanisms (including CD4
+ T cells, macrophage, neutrophil, and dendritic cell). Similar to COL1A1, higher expression of COL3A1 was associated with shorter overall survival in patients with ovarian carcinomas [
14]. CD36 is a membrane glycoprotein on platelets, monocytes and umbilical vein endothelial cells. CD36 could binds to collagen and have an important functions in cell adhesion process [
30]. In the previous reported [
15], the CD36-driven omental adipocytes metabolic reprogramming and functions in tumor-associated immune cells lead to tumor immune tolerance and tumor development, especially in ovarian carcinomas. Moreover, CD36 mediates immunological recognition, inflammation, cell adhesion, and apoptosis in pathogenesis of cancer. In conflict with the previous findings, our study demonstrated that the CD36 serve as a tumor suppressor which was down-regulated in CSCC when compared with Bowen disease. Cell adhesion to extracellular matrix is an important physiological stimulus for organization of the actin-based cytoskeleton [
31]. The tenascin family of extracellular matrix proteins includes Tenascin-C/R/X. Tenascin-C and Tenascin-X are expressed in several tissues during embryogenesis and in adult tissues undergoing active remodeling, such as tumors [
32]. Higher expression of TNC was correlated with a poorer prognosis in stages II and III of colorectal cancer and could serve as a diagnostic biomarker [
16]. Besides, the TNC may promote colorectal cancer progression and is involved in cancer stem cell-like properties via the Hedgehog signaling pathway [
33]. In addition, Xia S, et al. [
17] proved TNC knockdown cells were sensitive to Temozolomide therapy in glioblastoma. Our proteomics results also proved the TNC could driven the tumor progression in CSCC and this conclusion was consistent with the previous literature’s reported [
34].
FSCN1, an actin-bindling protein, identifies dendritic cells in the blood and in tissues. ACTN1, one of the alpha actinins, which belong to cytoskeletal proteins and perform important biological functions, such as cell adhesion and migration. Our proteomics results showed expression of FSCN1 and ACTN1 were significant higher in CSCC relative to Bowen disease, and FSCN1 as well as ACTN1 may related to the proliferation, invasion and migration in CSCC progression process. In the previous reported, the higher-regulation of FSCN1 indicates worse prognosis for patients with renal cell carcinoma [
18] and adrenocortical carcinoma [
19]. Zhang M, et al. [
18] indicated that higher expression of FSCN1 led to an up-regulation of MMP9 and N-Cadherin in renal cell carcinoma. Inhibition of PI3K/AKT or knockdown GSK-3b could decreased the expression of FSCN1, and then attenuated renal cell carcinoma invasion. On the other hand, Xie GF, et al. [
20] indicated the inhibition of ACTN1 could induce cell cycle arrest, promote apoptosis, and inhibit cell proliferation, migration, and invasion in the oral squamous cell carcinoma cell lines.
RAB31 belongs to the Rab family, mainly localized in the trans-Golgi network and endosomes, which is the largest Ras superfamily of small molecule GTP binding proteins. Accumulating reports has indicated that RAB31 is widely involved in the prognosis of various cancers, including pancreatic cancer [
22], cervical cancer [
23] and others. Higher expression of RAB31 was significant associated with shorter overall survival in pancreatic cancer [
22] and RAB31 knockdown could inhibited the epithelial-mesenchymal transition and cytoskeletal rearrangement in cervical cancer cells [
23]. However, little is known regarding the RAB31 expression levels in CSCC. Our study confirmed that up-regulation of RAB31 in CSCC relative to Bowen disease and RAB31 may play a crucial role in CSCC invasion, metastasis process. SERPINB1 is a member of the Serpin family of protease inhibitors and associated with multiple cancers progression. Huasong G, et al. [
24] suggested SERPINB1 could inhibited glioma migration and invasion probably by dampening the expression of matrix metalloproteinase-2. However, high expression of SERPINB1 in clinicopathologically invasive oral squamous cell carcinoma but not in normal oral mucosa (
P < 0.01) was found by Tseng MY. et al. [
35] Nevertheless, most study proved SERPINB1 may serve as a tumor suppressor and this conclusion was inconsistent with our results. Our study revealed that higher expression of SERPINB1 in CSCC relative to Bowen disease. This results may indicated the SERPINB1could as a novel therapeutic target to manage CSCC. In order to verify the effect of 8 proteins on the invasion and metastasis ability of CSCC and we selected the SERPINB1 for the next biomedical experiment. CSCC A431 cells were transfected with SERPINB1 small interfering RNA. After interfering with the expression of SERPINB1, the migration and invasion ability in the A431 cells were significantly decreased. This result indicated that inhibition of SERPINB1 can significantly inhibit the progression of CSCC. In addition, This result also demonstrated that 8 proteins may be related to the development of CSCC.
In conclusion, the proteomics technology provides a new method for the identification of key proteins associated with migration and invasion mechanisms in CSCC. These proteins were mainly involved in multiple pathways, including Focal adhesion, ECM-receptor interaction, Human papillomavirus infection, PI3K-Akt signaling pathway, PPAR signaling pathway, AMPK signaling pathway. Multiple protein factors, such as TNC, FSCN1, SERPINB1, ACTN1, RAB31, COL3A1, COL1A1 and CD36 could be as novel therapeutic target to manage CSCC. The most innovation of this manuscript was to explore the markers of CSCC progression using transcriptomics combined with proteomics methods in Chinese Han population. This also provides a theoretical basis for the targeted therapy of CSCC in the future.
Limitations
The numbers of samples in proteomics are insufficient and a larger cohort could be of benefit however sourcing human samples is a challenge.
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