Analysis of SEMA6B gene expression in breast cancer: identification of a new isoform

BACKGROUND: SEMA6B is a member of the semaphorins axon-guidance family. A growing body of evidence has been accumulated describing the role of semaphorin molecules in cancer development and the involvement of SEMA6B in cancer progression has recently been proposed. METHODS: Our analysis, based on real-time PCR, focused on the expression of SEMA6B in a panel of breast cancer tissues, compared to the normal counterpart. RESULTS: In cancer tissues we found a significantly strong down-modulation of this transcript. Moreover we identified and characterized a novel SEMA6B isoform, named SEMA6Ba. This isoform has a novel splice junction, created by the usage of alternative donor and acceptor splice sites internal to the exon 17. By in silico analysis we found that the new transcript 3' UTR lacks some highly-conserved miRNA binding sites, suggesting possible consequences on both spatial and temporal expression of SEMA6Ba. The translated sequence of SEMA6Ba lacks the cytoplasmic tail, crucial for triggering the reverse signaling described for the transmembrane semaphorins. We also demonstrated, by immunofluorescence analysis of endogenous and overexpressed SEMA6Ba, that the protein clearly localized to the endoplasmic reticulum and plasma membrane. In conclusion, SEMA6B gene products are strongly down modulated in breast cancer tissues and a new isoform named SEMA6Ba has been described and characterized. GENERAL SIGNIFICANCE: Our work states a clear relation among breast cancer and SEMA6B expression; moreover we describe for the first time the SEMA6Ba protein and report here the analysis of SEMA6Ba RNA messenger, the protein expression and the cellular localization.