Human Semaphorin 6B [(HSA)SEMA6B], A Novel Human Class 6 Semaphorin Gene: Alternative Splicing and All-Trans-Retinoic Acid-Dependent Downregulation in Glioblastoma Cell Lines

We have identified a novel human gene related to the class 6 semaphorin family of axon guidance molecules, termed human semaphorin 6B or (HSA)SEMA6B. Two splicing variants of this gene were identified by RT-PCR: (HSA)SEMA6B.1 (short isoform) and (HSA)SEMA6B.2 (longer isoform). Computational analysis suggests that these isoforms correspond to putative secreted and transmembranous semaphorins, respectively. The levels of (HSA)SEMA6B expression were evaluated by Northern blot analysis in different tissues and in some pathological and pharmacological conditions. We observed that (HSA)SEMA6B is highly expressed in human brain and at lower levels in a variety of other tissues. Interestingly, the (HSA)SEMA6B transcript was downregulated in two different human glioblastoma cell lines (T98G and A172) upon prolonged treatment with all-trans-retinoic acid, an anti-tumor and differentiation-inducing agent.