Gene expression profiling in human pituitary neuroendocrine tumours

Abstract

Introduction Pituitary neuroendocrine tumours (PitNETs), also referred to as pituitary adenomas, are the second most common primary brain tumours, which are clinically classified into various subtypes. Their formation, development, maintenance, proliferation, and immune evasion mechanisms are not yet fully understood. However, molecular strategies developed by the tumour microenvironment with the aim of reducing the efficacy and efficiency of the patient’s immune system have been hypothesized. These strategies involve the inactivation or diminished expression of genes within the PitNET microenvironment that are more prominently expressed within healthy pituitary tissue, or the increased expression of novel genes within the PitNET microenvironment that are not generally expressed within healthy pituitary tissue. Aim Information regarding the identity and expression of these genes is lacking, especially with regards to immune related genes. This knowledge gap could lead to a hindrance for novel therapies, including immunotherapies. Therefore, the present study aimed to determine how immune gene expression differs between two common PitNET subtypes, namely GH-secreting adenomas, and non-functioning pituitary adenomas (NFPAs). This level of expression was also compared to that of healthy pituitary tissue. Methods RNA-sequencing data from 29 PitNET and 1 healthy pituitary sample were processed via an RNA-sequencing workflow. A filtering strategy, including functional enrichment analysis, was then performed in which candidate immune system genes were chosen for validation by real-time quantitative PCR on a novel set of 14 adenomas. Results Differential gene expression analysis from RNA-sequencing data revealed 7945 genes (4460 upregulated and 3485 downregulated) which were filtered to six differentially expressed candidate genes. TYROBP, a novel gene for PitNETs, and CCL3 were significantly overexpressed in GH-secreting adenomas (60% and 80%, respectively). MADCAM1, also novel for PitNETs, was significantly overexpressed in NFPAs (67%). GATA3 expression did not significantly differ between the two subtypes. DEFA3 and CXCL9 were negligibly expressed in the two PitNET subtypes assessed. Reactome and KEGG highlighted possible pathways through which these genes could contribute to pituitary tumour microenvironment (TME) functioning. The most significant were ‘TH1 and TH2 cell differentiation’, ‘cytokine-cytokine receptor pathway’, and ‘chemokine receptors bind chemokines’. Conclusions Future studies on these genes, such as assessing their expression in other functioning PitNET subtypes, or examining the significant pathways in more detail are necessary to validate the results obtained. Based on these results, it was apparent that this study has successfully shed more light on some novel genes and can be considered as a basis for altering the understanding of not only PitNETs, but also other types of tumours.