Human fibulin-4: analysis of its biosynthetic processing and mRNA expression in normal and tumour tissues

Here, we report the identification of a human orthologue of fibulin-4, alon g with analysis of its biosynthetic processing and mRNA expression levels i n normal and tumour tissues. Comparative sequence analysis of fibulin-4 cDN As revealed apparent polymorphisms in the signal sequence that could accoun t for previously reported inefficient secretion in fibulin-4 transfectants. In vitro translation of fibulin-4 mRNA revealed the presence of full-lengt h and truncated polypeptides, the latter apparently generated from an alter native translation initiation site. Since this polypeptide failed to incorp orate into endoplasmic reticulum membrane preparations, it was concluded th at it lacked a signal sequence and thus could represent an intracellular fo rm of fibulin-4. Using fluorescence in situ hybridisation analysis, the hum an fibulin-4 gene was localised to chromosome 11q13, this region being synt enic to portions of mouse chromosomes 7 and 19. Considering the fact that t ranslocations, amplifications and other rearrangements of the 11q13 region are associated with a variety of human cancers, the expression of human fib ulin-4 was evaluated in a series of colon tumours. Reverse transcription-po lymerase chain reaction analysis of RNA from paired human colon tumour and adjacent normal tissue biopsies showed that a significant proportion of tum ours had similar to2-7-fold increases in the level of fibulin-4 mRNA expres sion. Taken together, results reported here suggest that an intracellular f orm of fibulin-4 protein may exist and that dysregulated expression of the fibulin-1 gene is associated with human colon tumourigenesis. (C) 2001 Fede ration of European Biochemical Societies. Published by Elsevier Science B.V . All rights reserved.