Dystroglycan is a receptor responsible for crucial interactions between extracellular matrix and cytoplasmic space. We provide the first evidence that dystroglycan is truncated. In HC11 normal murine and the 184B5 non-tumorigenic mammary human cell lines, the expected L L-dystroglycan 43 kDa band was found but human breast T47D, BT549, MCF7, colon HT29, HCT116, SW620, prostate DU145 and cervical HeLa cancer cells expressed an anomalous W W31 kDa L L-dystroglycan band. K K-Dystroglycan was udetectable in most of the cell lines in which L L-dystroglycan was found as a W W31 kDa species. An anomalous W W31 kDa L L-dystroglycan band was also observed in N-methyl-N-nitrosurea-induced primary rat mammary tumours. Reverse transcriptase polymerase chain reaction experiments confirmed the absence of alternative splicing events and/or expression of eventual dystroglycan isoforms. Using protein extraction procedures at low-and high-ionic strength, we demonstrated that both the 43 kDa and W W31 kDa L L-dystroglycan bands harbour their transmembrane segment. ß

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