Metastasis is the primary cause of mortality associated with cancer. Molecular mechanisms leading to metastatic spread are poorly studied. To get a better understanding of this process, we compared the gene expression pattern of two isogenic cell lines, HET-SR and HET-SR1 (Rous Sarcoma Virus-transformed embryo hamster fibroblasts) with different metastatic activity using the differential display technique. A novel cDNA of hamster gene shMDG1 (Syrian hamster homologue of microvascular differentiation gene 1), which had 94% homology with rat MDG1 gene, was identified. Expression of shMDG1 was increased in low metastatic HET-SR cell line in comparison to high metastatic HET-SR1. Sequence analysis of the ORF of shMDG1 gene showed that it belongs to the DnaJ/heat-shock proteins of 40 kDa (HSP40) chaperones family, considered to function as a cochaperone of HSP70 family. In order to confirm involvement of shMDG1 in metastasis, we injected parental and shMDG1 overexpressed cells into animals. We showed that overexpression of the shMDG1 gene significantly diminished the metastatic activity of both HET-SR and HET-SR1 cells. The shMDG1-induced repression of metastasis was not connected with alterations in cell proliferation and motility in vitro, but correlated well with a decrease in content of the Asn-linked beta1-6 branched oligosaccharides on cell surface.