Published in Cancer Detection and Prevention 1997; 21(2):158-166.

Β - 4 Integrin Subunit Expression is Downregulated in Low Metastatic Carcinoma Variants

L. Cimino, PhD, D. Perrotti, MD, G. D'Agostino, PhD, R. Falcioni, PhD, and A. Sacchi, PhD

Molecular Oncogenesis Laboratory, Regina Elena Cancer Institute, Rome, Italy

Address all correspondence and reprint requests to: Ada Sacchi, Ph.D., Laboratorio Oncogenesi Molecolare, Istituto Regina Elena per lo studio e la Cura dei Tumori, C.R.S., Via delle Messi D'Oro 156, 00158 Roma, Italia.

ABSTRACT: Organization and expression of the gene coding for Beta4 integrin subunit were investigated in murine carcinoma lines endowed with low and high metastatic potential maintained both in vivo and in vitro. Probes corresponding to either the extracellular or the cytoplasmic domains of the protein were generated and employed for Southern and Northern blot hybridization experiments. Southern blot analysis demonstrates a restriction fragment-length polymorphism between BALB/c and C57B1/6J DNAs. The different genomic organization of the Beta4 gene apparently does not generate variation in mRNA length. Northern blot analysis reveals a 7-kb transcript encoding full-length Beta4 protein and shorter transcripts that apparently correspond to nonfunctional mRNAs. In carcinoma cells endowed with low metastatic capacity, the 7-kb mRNA cannot be revealed in spite of the presence of shorter transcripts. In contrast, the 7-kb transcript is always present in tumor cells endowed with high metastatic capacity. Accordingly, the Beta4 protein is detectable, either by immunofluorescence or by Western blot analyses, only in highly metastatic carcinoma cells. In conclusion, the data presented show that in these murine carcinoma cell lines (i) the 7-kb mRNA is associated with a more invasive phenotype, and (ii) missing expression of the Beta4 integrin subunit in low metastatic carcinoma cells depends, at least in part, on mechanisms acting at a post-transcriptional level. The possibility that Beta4 subunit expression is a consequence of specific differentiation stages of lung carcinoma cells is discussed.

KEY WORDS: integrin, metastases, gene expression.