TI - Results . AB - Recently , we showed that CtBP1 expression is lost or strongly reduced in malignant melanoma leading to induction of MIA expression [4] . To find cellular mechanisms regulated by CtBP1 in melanoma we generated CtBP1 expressing melanoma cells by stable transfection to subsequently perform functional assays . The three cell clones selected show strong CtBP1 mRNA and protein expression (Fig 1A) . To confirm the regulation of MIA expression we performed quantitative RT-PCR and revealed a significant reduction of MIA expression in the CtBP1-expressing cell clones compared to mock controls ( Fig 1B ) . Proliferation and colony formation assays showed no difference in cell growth between CtBP1 expressing and the control clones ( data not shown ) . In contrast , reduction of migration ( Fig 2A ) and invasion in Boyden Chamber assays (Fig 2B) was observed suggesting that CtBP1 and CtBP1 -regulated genes control cellular migration . Interestingly , we observed a second minor signal in Western blotting , using the anti-CtBP1 antibody , approximately 5 kDa smaller than full length CtBP1 (RefSeq entry NM 001328) (Fig 1A) . To determine whether this band is due to an alternative splice product of CtBP1 we designed several sets of primer . Using these PCR primers and subsequent sequencing we show that melanoma cells express an alternative CtBP product lacking exon 4 ( CtBP1splice ) ( Fig 3A , B ) . Sequence analysis of genomic DNA revealed no mutations in splice sites causing the skipping of exon 4 in melanoma . The expression pattern of CtBP1splice in melanoma is demonstrated in Fig. 3A and revealed the expression of the splice variant in eight of eleven melanoma cell lines . The downregulation of full length CtBP1 in melanoma was previously shown [4] . This results in a protein missing aa 114-182 , which is the N-terminal region of the dehydrogenase homology domain and includes a PAK1 PHOSphorylation site (Fig 3C) . As the nature of this alternative splice product is completely unknown , we sought to determine whether CtBP1 binding to TCF4 ( which regulates MIA expression ) and Snail is intact . By co-immunoprecipitation we detected TCF4 and Snail binding to full length CtBP1 ( in the CtBP1-expressing melanoma cell clones ) , but none with CtBP1splice ( Fig 4A , B ) . This suggests that CtBP1splice can not modulate repressor activity on TCF4 and Snail , although other CtBP1 functions may be unaffected .