Accumulation of
hyaluronan has been demonstrated in the peritumoral
breast cancer stroma and nests of
tumor cells. In this study, we have quantified the production of
hyaluronan and the expression of mRNAs encoding
hyaluronan synthesizing (HAS) and
hyaluronan degrading (HYAL)
enzymes in a panel of
breast cancer cell lines. The analysis revealed that highly invasive
breast cancer cells produce high amounts of
hyaluronan and express preferentially HAS2
mRNA, whereas less invasive
breast cancer cells produce low amount of
hyaluronan and express HAS1 and HYAL1 mRNAs. We explored the importance of HAS2 expression for
breast cancer tumorigenicity, by specifically silencing the HAS2 gene using RNA interference (RNAi)-mediated suppression in the invasive
breast cancer cell line Hs578T. This led to a less aggressive phenotype of the
breast tumor cells, as assessed by cell growth, both in anchorage-dependent and anchorage-independent cultures.
siRNA-mediated knock down of HAS2 in Hs578T
breast tumor cells led to an up-regulation of HAS1, HAS3 and HYAL1 mRNAs, resulting in only a 50% decrease in the net
hyaluronan production; however, the synthesized
hyaluronan was of lower size and more polydisparse compared to control
siRNA-treated cells. Interestingly, Hs578T cells deprived of HAS2 migrated only half as efficiently as HAS2 expressing cells through cell-free areas in a culture wounding assay and through Transwell
polycarbonate membrane as well as invaded a
Matrigel layer. These results imply that alterations in HAS2 expression and endogenously synthesized
hyaluronan affect the malignant phenotype of Hs578T
breast cancer cells.