HSD11B2 gene encodes the type II isoform of 11-beta-hydroxysteroid dehydrogenase, a microsomal enzyme complex responsible for the interconversion of biologically active cortisol and inactive cortisone. This gene is highly expressed in kidney (highest expression) [22], colon [23], pancreas [24] and placenta [25]. According to the enzyme level expression profile of HSD11B2 from Protein Atlas (http://www.proteinatlas.org), HSD11B2 is downregulated in human skin squamous cell carcinoma and melanoma as well as in eight other cancer types [26]. To our knowledge, the underlying pathophysiological mechanism and clinicopathologic characteristics of HSD11B2 in melanoma has not been closely examined. Therefore, this study applied bioinformatics analysis using high-throughput RNA-sequencing data from TCGA to examine HSD11B2 expression in melanoma patients to demonstrate that low expression of HSD11B2 is mostly associated with direct extent of the primary tumour, degree of spread to regional lymph nodes, and age of melanoma patients. All these contributing factors significantly results in a low survivability. In addition, we discovered that changes HSD11B expression is associated with numerous receptors signalling pathways and multiple genes.
Anatomical extent of melanoma tumour and degree of spread to regional lymph nodes alongside increase of HSD11B2 gene expression are major contributing factors in lower predicted survivability of melanoma. Indeed, the thickness of the primary tumour is an important prognostic factor in predicting the risk that the cancer will spread. Melanoma skin cancer with tumour size less than 1 mm thick has a low chance of spreading, whereas tumour with more than 4 mm in thickness has a higher risk of spreading and recurrence [27]. Furthermore, prognosis is poorer if the cancer has spread to nearby lymph nodes which is an indication of metastasis stage which directly contributes to survivability. Interestingly, The Asian ethnic group has a higher contributing factor in lower survival rate. Though people of colour are less likely to became afflicted with melanoma, they are more likely to die from it due to delay in detection and presentation. This may be associated with lack of awareness, diagnosis at more advanced stage and socioeconomic barriers hindering access to care [28].
Our study revealed that patients with melanoma tumour has a lower HSD11B2 expression, as well as a lower predicted survivability. Type I and Type II 11-beta-hydroxysteroid dehydrogenase encoded by the HSD11B1 and HSD11B2 gene respectably governs the glucocorticoid action on target tissues. Glucocorticoid are a class of steroid hormones that is vital in regulation of stress responses, metabolism and immune homeostasis [29]. HSD11B1, functions as a reductase and catalyses the regeneration of active glucocorticoids, thus amplifying cellular action. On the other hand, HSD11B2 is a high-affinity dehydrogenase that inactivates glucocorticoids [30]. Therefore, 11-beta-hydroxysteroid dehydrogenase are important enzymes in the tissue-specific regulation of glucocorticoids, with reports suggesting that alteration in regulation of 11-beta-hydroxysteroid dehydrogenase is related to numerous pathological process in the skin such as wound healing, cell motility, scar formation and remodelling and promotion of terminal epidermal differentiation [31–34]. A study by Cirillo et al. (2017) demonstrated that HSD11B2 is synthesised by human malignant keratinocytes (epidermis cells that forms barriers against environmental damages such as UV radiation, heat, and viruses [26]. The same report also revealed that a significant downregulation of HSD11B2 was observed in human skin squamous cell carcinoma and demonstrated that skin cancer cells have the ability to regulate cortisol levels through expression of both HSD11B1 and HSD11B2 levels. Similarly, downregulation of HSD11B2 mRNA has also been reported in skin lesions of leprosy patients compared to normal skin [35]. Multiple types of cancers such as colorectal cancer [36] and oral cancer [33] also displays a trend of downregulated HSD11B2 expression. These evidences agree with our results and highlights the importance of HSD11B2 in the glucocorticoid system and its potential significance in melanoma.
As shown by our results, changes in the expression of HSD11B2 is co-associated with nine other genes. Among these, ATP6V1B1 (positively correlated with HSD11B2) is a gene that encodes a component of vacuolar ATPase, an enzyme which mediates acidification of eukaryotic intracellular organelles [37]. This acidification influences a wide range of cellular process, many of which are dysregulated in cancers [38]. Dysregulation of vacuolar ATPase and its association to numerous cancers was a conclusion made based on altered expression of specific vacuolar ATPase subunits in malignant cells and clinical features of cancer. For Instance, a study concluded that the downregulation of vacuolar-ATPase subunit ATP6V1B1 leads to resistant mechanism of trastuzumab mediated antibody dependent cellular cytotoxicity in human breast cancer cell line (HER2 overexpressing)[39]. Analysis of the TCGA database also revealed that amplification or overexpression of ATP6VC1 (gene that codes for the C subunit of vacuolar ATPase) was observed in 34% of human breast cancer resulting in low survivability [40]. Other studies revealed expression of vacuolar ATPase specific subunits in other forms of cancers such as pancreatic cancer [41], lung cancer [42], oral squamous cell carcinoma [43, 44], ovarian cancer [45] and cervical cancer [46]. Therefore, it is likely that ATP61B1 also plays a role in melanoma and its association with HSD11B2 requires further investigation. Another gene that was positively associated to HSD11B2 expression changes was KRT19. KRT19 referred to Keratin 19, is a member of the acidic type 1 cytokeratin family protein that is expressed predominantly in various cells types in the epithelium [47–49]. Since 80% of cancers are of epithelial cells in origin [50, 51], Keratins are widely used as diagnostic markers to detect tumours in both primary and distal sites and to determine the tissue of origin of the tumour for the purpose of assisting in treatment strategies [52]. In this context, KRT19 has been suggested to be one of the more sensitive diagnostic markers across a broad range of cancer types. Indeed, studies indicated that KRT19 is highly expressed in breast, colon, liver, and intestine cancer, and also associated with poor clinical outcomes in patients [53–56]. Since activated keratinocytes expresses various forms of keratin proteins (KRT6 KRT16 and KRT17), the association of KRT19 expression to HSD11B2 is an underlying molecular mechanism that needs to be examined in future melanoma researches.
Numerous pathways were revealed to perturbate between HSD11B2 low expression and high expression phenotype via the GESA pathway analysis of TCGA data. Among these pathways, the cytosolic DNA sensing pathway (cGAS–STING pathway) is part of the innate immune system which recognises presence of cytosolic DNA, trigger expression of inflammatory genes (leading to senescence) and activates defence mechanisms [57]. Numerous studies have indicated that tumour cells developed strategies to inhibit DNA sensing pathway activation, likely for immune evasion during carcinogenesis in colorectal carcinoma and melanoma [58, 59]. The JAK-STAT signalling pathway is another pathway closely related in the process such as immunity, cell death and tumour formation. Disruption in JAK-STAT signalling may lead skin conditions, cancers, and disputed immune systems [60]. Indeed, a study by Pansky et al. (2000) hypothesizes that defective signal transduction through the JAK-STAT pathway could contribute to the poor response rate of interferons (antiviral, antiproliferative and immunomodulatory protein) treatment in patients with advanced melanoma [61]. Both the NOD like receptor signalling pathway and toll-like receptor signalling pathway were detected to be differentially expressed in relationship to changes in HSD11B2. These pathways belongs to families of the innate immune system. Activation of these immune pathways leads to a broad range of pro- and/or anti-inflammatory signals, including the secretion of interferons, tumour necrosis factors and cytokines [62]. Disruption in these signals may result in chronic inflammatory states that directly affect cell cycle progression and apoptosis which subsequently creates an environment for diseases, such as cancer [62, 63]. Based on the presented evidence, all the identified pathways revealed by our results plays major roles in cancer and highlights the importance of their association with HSD11B2 expressional changes in melanoma for future researches.