Expression of T‐type calcium channel splice variants in human glioma

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Abstract
In humans, three isoforms of the T-type (Cav3.1) calcium-channel α1 subunit have been reported as a result of alternate splicing of exons 25 and 26 in the III–IV linker region (Cav3.1a, Cav3.1b or Cav3.1bc). In the present study, we report that human glioma express Cav3.1 channels in situ, that splicing of these exons is uniquely regulated and that there is expression of a glioma-specific novel T-type variant (Cav3.1ac). Seven human glioma samples were collected at surgery, RNA was extracted, and cDNA was produced for RT-PCR analysis. In addition, three glioma cell lines (U87, U563, and U251N), primary cultures of human fetal astrocytes, as well as adult and fetal human brain cDNA were used. Previously described Cav3.1 splice variants were present in glioma samples, cultured cells and whole brain. Consistent with the literature, our results reveal that in the normal adult brain, Cav3.1a transcripts predominate, while Cav3.1b is mostly fetal-specific. RT-PCR results on glioma and glioma cell lines showed that Cav3.1 expression in tumor cells resemble fetal brain expression pattern as Cav3.1bc is predominantly expressed. In addition, we identified a novel splice variant, Cav3.1ac, expressed in three glioma biopsies and one glioma cell line, but not in normal brain or fetal astrocytes. Transient expression of this variant demonstrates that Cav3.1ac displays similar current-voltage and steady-state inactivation properties compared with Cav3.1b, but a slower recovery from inactivation. Taken together, our data suggest glioma-specific Cav3.1 gene regulation, which could possibly contribute to tumor pathogenesis.