Aim. To study the effect of heparin, as a factor of tumor microenvironment, on the expression of ERVW-1 locus and CHI3L1 gene, involved in increasing of cancer cells metastatic potential, in U-87 MG (U87) and U-251 MG (U251) gliotblastoma cells. Methods. U87 and U251 cells were cultured with or without the addition of heparin to the cultural medium. Total cellular RNA was isolated and used for cDNA synthesis and subsequent PCR with primers to different regions of ERVW-1 and CHI3L1. Results. Both U87 and U251 cells showed high level of expression of full-length ERVW-1 RNA. But only in U251 cells inhibition of the full-length transcript by heparin was revealed. Spliced isoform hasn’t been detected in any of variants. Though the solely env gene transcript expressed at low level in both lines and was inhibited similarly by heparin. Expression of CHI3L1 has been detected in both lines with primers towards exons 4-5 with some lowering in level under the heparin influence. Only in U87 cells the PCR-fragment with primers to exons 8-9 has been detected. In control U87 cells hypothetic spliced isoform of CHI3L1 transcript has been revealed with primers to exons 1-9. Conclusions. Heparin has complex and cell line-dependent regulation of expression of ERVW-1 locus and CHI3L1 gene in the glioblastoma cell lines U87 and U251.
 Keywords: glioblastoma, heparin, ERVW-1, CHI3L1.