Cripto-1 inhibits beta-casein expression in mammary epithelial cells through a p21ras-and phosphatidylinositol 3'-kinase-dependent pathway.
Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that does not directly activate any of the known erbB type 1 tyrosine kinase receptors. Also, CR-1 stimulates the growth of HC-11 mouse mammary epithelial cells. We found that prior treatment of HC-11 cells with exogenous CR-1 induced a competency response to the lactogenic hormones dexamethasone, insulin, and prolactin (DIP) with respect to the induction of the milk protein beta-casein. In contrast, simultaneous treatment of mouse HC-11 cells with CR-1 in the presence of DIP inhibited beta-casein expression. The inhibitory effects of CR-1 on beta-casein expression in response to DIP were not unique to this mouse mammary epithelial cell line, because beta-casein and whey acidic protein expression in primary mouse mammary explant cultures established from midpregnant mice were also differentially inhibited by several epidermal growth factor-related peptides including CR-1. The mitogenic and differentiation effects of CR-1 are mediated by the binding of CR-1 to a cell surface receptor that is known to activate the ras/raf/mitogen-activated protein kinase (MAPK)/MAPK kinase pathway. The inhibitory response of CR-1 in HC-11 cells on beta-casein expression after treatment with DIP can be attenuated by B581, a peptidomimetic farnesyltransferase inhibitor that blocks p21ras farnesylation and activation, and by the phosphatidylinositol 3'-kinase (PI3k) inhibitor LY 294002 but not by PD 98059, a MAPK kinase inhibitor that blocks MAPK activation. These data suggest that the ability of CR-1 to block lactogenic hormone-induced expression of beta-casein is mediated through a p21ras-dependent, PI3k-mediated pathway. This is further substantiated by the observation that CR-1 is able to stimulate the tyrosine phosphorylation of the p85 PI3k regulatory subunit and to increase the activity of PI3k in HC-11 cells.
De Santis
M L
ML
Tumor Growth Factor Section, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
Kannan
S
S
Smith
G H
GH
Seno
M
M
Bianco
C
C
Kim
N
N
Martinez-Lacaci
I
I
Wallace-Jones
B
B
Salomon
D S
DS
D000818:Animals; D002364:Caseins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects* / Q000502:physiology; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004815:Epidermal Growth Factor; D004847:Epithelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006133:Growth Substances / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000378:metabolism; D008562:Membrane Glycoproteins; D051379:Mice; D009363:Neoplasm Proteins / Q000494:pharmacology*; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011388:Prolactin / Q000494:pharmacology; D015398:Signal Transduction
D002364:Caseins; D006133:Growth Substances; D007328:Insulin; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; C489450:Tdgf1 protein, mouse; D004815:Epidermal Growth Factor; D003907:Dexamethasone; D011388:Prolactin; D019869:Phosphatidylinositol 3-Kinases; D015689:Oncogene Protein p21(ras)