Identification and characterisation of calcitonin receptor isoforms expressed in glioblastoma derived glioma stem and U‐87 MG cells

Glioblastoma (GBM) is a highly lethal brain cancer in which the calcitonin receptor (CT Receptor), encoded by the CALCR gene, is expressed in 78–88% of patient biopsies. Here, we investigate whether the CT Receptor plays a role in cancer cell survival. In cancer cell lines, knockdown of CALCR disrupts the cell cycle and induces apoptosis, supporting an essential pro‐survival role. The CALCR gene produces three main transcripts in humans, of which Transcript 1 encodes CALCR _b mRNA including exon 10 and is translated into the CT _b Receptor isoform, and Transcripts 2 and 3 which are translated into the CT _a Receptor. CALCR _b expression is conserved across a diverse range of mammalian species. We examined the expression of all CT Receptor isoforms ( CALCR _total ) and CALCR _b expression in four high‐grade glioma stem‐like cell lines and in U‐87 MG glioblastoma cells. Using qPCR, we observed stable levels of both CALCR _total and CALCR _b expression under conditions of autophagy or apoptosis, consistent with a requirement for CALCR _b in cell survival. As alternative splicing (AS) of key genes in cancers confers tumour resilience, we investigated AS of CALCR transcript 2 using long‐read nanopore sequencing. Unexpectedly, we discovered a novel AS event causing inclusion of exon 10 within Transcript 2 in all glioblastoma cell lines investigated. This finding, together with stable CALCR _b expression under cellular stress and the finding by other groups confirming that knockdown of CT Receptor compromises cell survival, implicates the CT _b Receptor as a potential oncoprotein.