Association of pS2 (TFF1) release with breast tumour proliferative rate: in vitro and in vivo studies

Although cytosolic expression of the protein pS2 (TFF1) is considered to be a marker of oestrogen receptor (OR) function, there exists some clinical data to suggest an inverse relationship of cytosolic pS2 to tumour proliferation. Although secreted from breast cancer cells, the relationship of pS2 secretion to tumour natural history has been little studied. The mechanisms and kinetics of pS2 release and its relation to tumour cell proliferation were studied in a human breast cancer cell line MCF-7 and verified in a preliminary clinical study. Stimulation by stripped serum or oestradiol resulted in parallel increases of proliferation and pS2 release in both time course and dose-response experiments. Direct pharmacological alterations of proliferation were followed by identical changes in pS2 release. The relationship between serum pS2 levels and tumour proliferative activity when analysed as a function of steroid status showed a slope of 0.56 in OR+ vs. 0.19 in OR- tumours. It is concluded that pS2 release from breast cancer cells is associated with their proliferation and measurement of serum pS2 levels might be a good predictor of tumour proliferative state and could permit noninvasive monitoring of this tumour parameter.

Release of the aspartyl protease cathepsin D is associated with and facilitates human breast cancer cell invasion

Data concerning the hormone sensitivity of the release and role of the aspartyl protease cathepsin D in tumor proliferative and invasive processes have been contradictory. To clarify the mechanisms of its release and role we first studied the contribution of estradiol and stripped serum to the time course and kinetics of cathepsin D release, proliferation, and invasion in parallel in the MCF-7 in vitro breast cancer cell culture model. Both estradiol and stripped serum independently stimulated both proliferation and cathepsin D release. However, the dose-response of estradiol and stripped serum-dependent stimulated release were similar to those for invasion and differed from those for proliferation: cathepsin D release and invasion were first stimulated at a stripped serum concentration more than 10-fold lower than that which initiated proliferation and had half stimulation constants almost 10-fold lower than those for proliferation. These results demonstrate that cathepsin D release is not related in any direct way to proliferation. The effect of the reduction of cathepsin D activity or release on in vitro invasion was also measured: both the inhibition of secreted cathepsin D activity by a specific inhibitor, diazoacetyl-DL-Nle-OMe, and the reduction of cathepsin D release by antisense oligonucleotides against its translation start site reduced cellular in vitro invasion without affecting proliferation. Cathepsin D release and activity are concluded to be directly involved in the process of invasion.

Cytokeratins and proliferation in breast cancer patients

Tissue polypeptide antigen (TPA) was studied in 242 sera and 165 tumor cell cytosols (both evaluations in 67 cases) of breast cancer patients, for which proliferative activity, determined by the TLI technique, was also available. The TPA serum and tumor cell cytosol median values (utilized for measure analysis as cut-off) were 70 U/1 and 377 U/mg cytosol protein, respectively. High serum TPA levels were associated with unfavourable clinicopathological characteristics whereas a higher tumor cell cytosol TPA level was associated with better cytohistological tumor differentiation. Furthermore, no overall correlation was found between serum and tumor cell cytosol TPA levels or between their levels and TLI. When analyzing cases in which serum and tumor cell cytosol TPA values were higher than 100 U/l and 500 U/mg cytosol protein, respectively (n = 28), serum TPA was positively associated with TLI (slope = 12.3 r = 0.55, p < 0.01), while cytosolic TPA resulted negatively associated with TLI (slope = -87.4 r = 0.41, p < 0.01). Finally, a strong inverse relationship between cytosolic and serum TPA (p < 0.0005) became evident. We suggest that TPA could represent a serum marker for tumor cell proliferation in specific patient subgroups with original high serum and/or cytosol TPA expression.

Differential responsiveness of proliferation and cytokeratin release to stripped serum and oestrogen in the human breast cancer cell line, MCF-7

In vitro research into hormone sensitivity and the relation to proliferation of cytokeratin release from cancer cells is scarce. Therefore, we examined the stimulation of proliferation and the release of cytokeratins in a breast cancer cell culture model. Cell growth was stimulated by 17 beta-oestradiol (10(-11) M), stripped serum (10%) and by the two together. Cytokeratin release was stimulated only by stripped serum, oestradiol having no effect. After long incubation periods (> 12 h), cytokeratin release also commenced in the control and oestradiol treatments. Release rate versus time analysis suggested that there are two different release processes. Cytokeratin release was first stimulated at a stripped serum concentration approximately 100 times lower than that which initiated proliferation. Pharmacological alteration of proliferation with cordyceptin resulted in growth changes without alterations in cytokeratin release. We conclude that cytokeratin release in these cells is unrelated to proliferation, independent of oestrogen action and probably in some way related to growth factor receptor function.

pS2--a new cytosolic protein recognized by monoclonal antibodies as a marker of hormone sensitivity in breast cancer

Using a new immunoradiometric assay (ELSA pS2 Cis-France), a total of 200 cytosols obtained from primary breast tumors were examined for pS2 content, which is an estrogen-regulated protein actually studied as a marker of hormone sensitivity and favorable prognostic factor in breast cancer. In our patient group, the median pS2 value corresponding to 5.3 ng/mg of cytosolic proteins was used as cutoff. pS2 content was not related to menopause status, tumor size, or nodal involvement, whereas a positive correlation was found between pS2 and ER/PgR status. Moreover, the association of pS2 with steroid receptors seems to identify subgroups of patients better than ER/PgR alone.

Cytosolic levels of estrogen-regulated pS2 protein in breast cancer: correlation with tumor proliferative activity

Using a new immunoradiometric assay, a total of 100 cytosols obtained from primary breast tumors were examined for content of pS2, an estrogen-regulated protein. In our series, the median pS2 value was 5 ng/mg protein cytosol which was used as the cut-off. pS2 content was not correlated with menopausal status, tumor size, nodal involvement or tumor proliferative activity expressed as labeling index (tritiated thymidine LI). A positive correlation was found between pS2 and estrogen (ER) and progesterone (PgR) hormone receptors. pS2 in association with ER and PgR seems to identify tumor subgroups with diverse hormone responsiveness. Moreover, in favorable and unfavorable prognostic subgroups, LI and pS2 further emphasize this prognostic diversity.