Pivotal role of tyrosine phosphatase SHP-1 in AT2 receptor-mediated apoptosis in rat fetal vascular smooth muscle cell.
OBJECTIVE
To examine the possible crosstalk and the roles of angiotensin (Ang) II type 1 (AT1) and type 2 (AT2) receptors in the control of apoptosis in fetal vascular smooth muscle cells (VSMCs).


METHODS
Fetal VSMCs were prepared from rat fetal aorta at embryonic day 20. Expression of Ang II receptors was measured by a radioligand binding assay. Apoptotic changes were assessed by caspase 3 activity and chromatin dye staining. Regulation of extracellular signal-regulated kinase (ERK) activity via Ang II receptors was analysed by determining phosphorylated ERK with Western blot. Ang II receptor-mediated activation of tyrosine phosphatase SHP-1 was assessed by protein tyrosine phosphatase assay.


RESULTS
The expression of AT1 and AT2 receptors was approximately 70%: 30% per cell. Serum depletion induced apoptosis in fetal VSMCs and selective AT1 receptor stimulation attenuated the apoptotic changes, whereas selective AT2 receptor activation enhanced apoptosis. Ang II increased ERK phosphorylation, which was inhibited by addition of the AT1 receptor-specific antagonist CV11974, but enhanced by addition of the AT2 receptor-specific antagonist PD123319, suggesting that activation of AT2 receptor attenuated the AT1 receptor-mediated ERK phosphorylation. Moreover, we demonstrated that AT2 receptor stimulation activated SHP-1 in fetal VSMCs, whereas AT1 receptor stimulation did not. Transient transfection of a dominant-negative SHP-1 mutant into rat fetal VSMCs resulted in a significant decrease of the AT2 receptor-mediated inhibition of ERK phosphorylation and attenuated the proapoptotic effect of AT2 receptor.


CONCLUSIONS
These results indicate that a crosstalk between AT1 and AT2 receptors regulates the survival of fetal VSMCs and substantiate SHP-1 as a key molecule in AT2 receptor signaling.
Department of Medical Biochemistry, Ehime University School of Medicine, Shigenobu, Onsen-gun, 791-0295, Ehime, Japan.
T
T
Cui
H
H
Nakagami
M
M
Iwai
Y
Y
Takeda
T
T
Shiuchi
L
L
Daviet
C
C
Nahmias
M
M
Horiuchi
D000704:Analysis of Variance; D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D004789:Enzyme Activation; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000196:embryology* / Q000201:enzymology; D010766:Phosphorylation; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin / Q000378:metabolism*
D047908:Intracellular Signaling Peptides and Proteins; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D020928:Mitogen-Activated Protein Kinases; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C509250:Ptpn6 protein, rat