Convergence of Progesterone and Epidermal Growth Factor Signaling in Breast Cancer

Abstract

During late stages of breast cancer progression, tumors frequently acquire steroid hormone resistance with concurrent amplification of growth factor receptors; this alteration predicts a poor prognosis. We show here that following treatment with the progestin, R5020, breast cancer cells undergo a "biochemical shift" in the regulation of epidermal growth factor (EGF)-stimulated signaling pathways: R5020 potentiates the effects of EGF by up-regulating EGFR, c-ErbB2 and c-ErbB3 receptors, and by enhancing EGF-stimulated tyrosine phosphorylation of signaling molecules known to associate with activated type I receptors. Independently of EGF, R5020 increases Stat5 protein levels, association of Stat5 with phosphotyrosine-containing proteins, and tyrosine phosphorylation of JAK2 and Shc. Furthermore, progestins "prime" breast cancer cells for growth signals by potentiating EGF-stimulated p42/p44 mitogenactivated protein kinase (MAPK), p38 MAP kinase, and JNK activities. Although the levels of cyclin D1, cyclin E, and p21 WAF1 , are up-regulated by R5020 alone, they are synergistically up-regulated by EGF in the presence of R5020. Up-regulation of cell cycle proteins by EGF is blocked by inhibition of p42/p44 MAPK only in the presence of R5020, supporting a shift in the regulation of these cell cycle mediators from MAPK-independent to MAPK-dependent pathways. In summary, progesterone selectively increases the sensitivity of key kinase cascades to growth factors, thereby priming cells for stimulation by latent growth signals. These data support a model in which breast cancer cell growth switches from steroid hormone to growth factor dependence.Estradiol and progesterone are involved in breast cancer development, but at the time of diagnosis only one-third of tumors are steroid hormone-dependent. As they progress, these tumors often acquire steroid hormone resistance, yet retain nuclear steroid receptors. Indeed, nuclear receptor loss or mutation accounts for only 10 -20% of steroid hormone-resistant tumors (1). Thus, it has been postulated that in the majority of resistant tumors, control over growth is assumed by locally acting autocrine or paracrine peptide growth factors. As a result, invasive cancers with the worst prognosis are those that are growth factor receptor positive and steroid hormone resistant (2). Growth factors regulate cell growth by activating intracellular signal transduction pathways after binding to high affinity tyrosine kinase receptors on the cell surface. Steroid hormone receptors are ligand-activated nuclear transcription factors. Herein, we sought to understand how these two separate pathways converge to regulate breast cancer cell growth.The mechanisms by which growth factors stimulate cell proliferation are complex. Growth factors induce receptor dimerization and activation of intrinsic tyrosine kinase activity. Autophosphorylation of tyrosine residues located in the cytoplasmic domain of the receptors stimulates binding of specific regulatory proteins via their SH2 1 and SH3 domains, which ...

Age-dependent decline in EGF-induced signaling is independent of intracellular thiols

“…As shown in Figure 2, ERK-MAP kinase is activated eleven-fold in response to EGF treatment in cells from young animals. These results are similar to those reported for other cell types (7,24). In hepatocytes from old rats, this activation is diminished to 5-fold over basal levels (15,25).…”

C‐myc gene expression alone is sufficient to confer resistance to antiestrogen in human breast cancer cells

“…For example, epidermal growth factor (EGF) is required for cyclin D 1 expression. 48 Progesterone, likely removed by our dextran-charcoal procedure, was reported to increase the sensitivity of key kinase pathways to polypeptide growth factors. Progestins were able to prime breast cancer cells by potentiating the EGF-stimulated p42/ ng/ml TNF-␣ plus 10 g/ml cycloheximide (TNF).…”

“…p44 mitogen-activated protein kinase, p38 MAP kinase and JNK activities. 48 Finally, insulin and IGF-I that are known to be important for breast cancer cell growth, were also removed from FBS by dextran-charcoal. 46,49 In conclusion, we have successfully developed a novel human breast cancer cell model in which the expression of c-myc can be stringently and rapidly regulated.…”

Linkage of progestin and epidermal growth factor signaling: Phosphorylation of progesterone receptors mediates transcriptional hypersensitivity and increased ligand-independent breast cancer cell growth

“…PR Ser294 is a hormone-inducible MAPK consensus site in the PR N-terminus that may serve as a direct "sensor" for MAPK-dependent input to PR transcriptional activity (6,(13)(14)(15)(16)19,32). Therefore, we included our well-characterized S294A PR mutant receptor in the above experiments (Fig.…”

“…Cross-talk between EGF and ovarian steroid hormone receptors likely continues in the malignant breast. Indeed numerous points of cross-talk between estrogen and progesterone and growth factor signaling events have been described (4)(5)(6)(7). Additionally, progesterone addition to estrogen in hormone replacement therapy increases breast cancer risk (8,9).…”