Laminin alpha chains in colon carcinoma cell lines: detection of a truncated laminin alpha1 mRNA in Caco-2 cells.
Changes in basement membrane structure are known to accompany carcinoma formation. We analyzed laminin alpha1 and alpha5 chains in colon carcinoma cell lines. Variable levels of the Mr 380,000 alpha5 laminin protein and 11-kb alpha5 laminin mRNA were noted. In contrast, laminin alpha1 protein was not synthesized by any of the colon carcinoma cell lines tested. Northern blotting revealed expression of a 10-kb laminin alpha1 mRNA only in control cells. Unexpectedly, expression of a truncated laminin alpha1 message of approximately 8 kb was found in one cell line, the adenocarcinoma cell line Caco-2. By RT-PCR and Northern blotting a deletion in the laminin alpha1 mRNA was mapped to the 5' end, spanning nucleotides 41-1835. The deletion spans the translation start site, explaining the complete lack of the protein. Southern blotting of genomic Caco-2 DNA did not reveal any larger truncation, suggesting a point mutation manifested at the posttranscriptional level. The identified truncation is the first genetic defect described for the laminin alpha1 chain and suggests that mutations in the LAM A1 gene might underlie the observed lack of the laminin alpha1 chain in some colon carcinomas.
Velling
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Department of Animal Physiology, Uppsala University, Uppsala, S-751 24, Sweden.
Tiger
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Ekblom
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Gullberg
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D018938:Caco-2 Cells; D002277:Carcinoma / Q000235:genetics*; D003110:Colonic Neoplasms / Q000235:genetics*; D019073:HT29 Cells; D006801:Humans; D007797:Laminin / Q000235:genetics* / Q000302:isolation & purification; D017354:Point Mutation; D012333:RNA, Messenger / Q000235:genetics*; D017384:Sequence Deletion; D014158:Transcription, Genetic
D007797:Laminin; D012333:RNA, Messenger; C097043:laminin alpha5; C084098:laminin A