Heregulin inhibits proliferation via Erks and Phosphatidyl Inositol 3-kinase activation but regulates Urokinase Plasminogen Activator independently of these pathways in metastasic mammary tumor cells

L PURICELLI, C J PROIETTI, L LABRIOLA, M SALATINO, M E BALAÑÁ, J AGUIRRE GHISO, R LUPU, O P. PIGNATARO, E H. CHARREAU, E BAL DE KIER JOFFÉ, P V ELIZALDE

INTERNATIONAL JOURNAL OF CANCER. JOURNAL INTERNATIONAL DU CANCER.

Año: 2002 p. 642 - 653

0020-7136

Heregulin (HRG) and type I receptor tyrosine kinases (RTKs) expressions were investigated in the highly invasive and metastatic LM3 cell line, our previously described model of metastasis for mammary cancer (Bal de Kier Joffe et al., 1986; Urtreger et al., 1997). While LM3 cells do not express HRG, they show presence of high levels of ErbB-2 and ErbB-3 as well as moderate expression of ErbB-4. Addition of exogenous HRGb1 resulted in inhibition of both proliferation and migration of LM3 cells. HRGb1 was also able to decrease the activity of urokinase-type plasminogen activator (uPA) and matrix metalloproteinase 9 (MMP-9), two key enzymes to the invasion and metastatic cascade. HRGb1 treatment of LM3 cells induced tyrosine phosphorylation of ErbB-2, ErbB-3 and ErbB-4 as well as the formation of ErbB-2/ErbB-3 and ErbB-2/ErbB-4 heterodimers. Assessment of the signaling pathways involved in HRGb1 action indicated that HRGb1 addition to LM3 cells resulted in activation of phosphaptidylinositol 3- kinase (PI-3K) and in strong induction of the association of the p85 subunit of PI-3K with ErbB-3. HRGb1 also caused the rapid activation of ERK1/ERK2 and of Stat3 and Stat5 (signal transducers and activators of transcription, STATs). This is the first demonstration of HRGb1 capacity to activate STATs in mammary tumor cells. Blockage of PI-3K activity with its chemical inhibitor wortmannin, or of MEK1/ERKs activity with PD98059, resulted in suppression of HRGb1 ability to inhibit LM3 cell growth. Notwithstanding the suppression of these two signaling pathways, HRGb1 still proved capable of inhibiting uPA activity. Therefore, our results provide evidence that signaling pathways involved in HRGb1-regulated  inhibition of proliferation appear to be distinct from those involved in HRGb1 regulation of uPA, a  protease that plays a pivotal role in invasion and metastasis