CD44 interactions with hyaluronan decrease the metastatic potential of breast cancer cells
Authors: Jose Lopez, Todd D. Camenisch, Mark V. Stevens, Barbara J. Sands, John McDonald, Joyce A. Schroeder
Journal: Cancer Research (2005)

Proc Amer Assoc Cancer Res, Volume 46, 2005

5244 

CD44 is an adhesion molecule present on a wide variety of cells, including mammary epithelial tumor cells. However, the role of CD44 in tumor progression is a controversial one. While many believe CD44 to promote tumor progression, others believe CD44 is not involved in tumor progression and may even be protective against invasion. To firmly establish the role of CD44 in breast cancer metastasis, MMTV-PyMT transgenic and MMTV-PyMT CD44-/- bitransgenic mouse tumor progression and metastatic lung tumor formation were evaluated. No difference was observed in the rate of primary tumor formation. However, MMTV-PyMT CD44-/- bitransgenic mice had a 67% incidence of metastasis compared to a 16% incidence on the MMTV-PyMT control mice. Additionally, the average number of metastatic tumors per mouse was also higher in the in the CD44 null mice. Together these findings suggests that CD44 does not play a role in tumor progression, but rather, plays a role in delaying metastatic tumor formation. To resolve the cause of the increased number of metastatic pulmonary tumors in the absence of CD44, we have looked at the expression patterns of the CD44 and its ligand Hyaluronan (HA). CD44 expression is found throughout the mammary tumor epithelium while HA expression is limited to the stromal area surrounding the tumor. This led us to investigate which cells may be responsible for HA production in mammary tumor tissue through the use of an MMTV-PyMT Has2-GFP bitransgenic mice. The Has2-GFP mouse expresses GFP under the control of the promoter for an HA producing enzyme, Has2. Anti-GFP staining shows tumor epithelial cells do not produce HA. Rather, cells within the stromal compartment surrounding the tumor are responsible for Has2 mediated HA production. Since HA production is mediated by stromal cells we designed an invasion assay that would mimic cellular invasion into a 3 dimensional matrix that contained immobilized HA similar to the stromal compartment surrounding tumors. We subjected 3 CD44 positive metastatic breast cancer cell lines to the assay. In each case invasion into gels cast with HA occurred at a rate significantly lower than invasion into gels that contained no HA. These result suggest that the presence of HA in a matrix may function to inhibit cellular invasion. To test whether HA mediated inhibition of invasion was a CD44 dependant event, we incubated the invasive breast cancer cell line MDA-MB-231 with a CD44 blocking antibody prior to the addition to the invasion assay. Invasion into gels containing no HA did not differ with or withoutwithout the blocking antibody. However, cellular invasion into gels containing HA was higher in the presence of the blocking antibody. In fact, invasion into HA containing gels with the blocking antibody was even higher than into gels that contained no HA. Therefore, while HA may inhibit cellular invasion in the presence of CD44, the absence of CD44 may promote HA mediated invasion.