Mutant p53 Disrupts Role of ShcA Protein in Balancing Smad Protein-dependent and -independent Signaling Activity of Transforming Growth Factor-β (TGF-β)

Shu Lin,Lan Yu,Junhua Yang,Zhao Liu,Bijal Karia,Alexander J.R Bishop,James Jackson,Guillermina Lozano,John A Copland,Xiaoxin Mu,Beicheng Sun,Lu-Zhe Sun

doi:10.1074/jbc.m111.265397

Abstract

Biomarkers are lacking for identifying the switch of transforming growth factor-β (TGF-β) from tumor-suppressing to tumor-promoting. Mutated p53 (mp53) has been suggested to switch TGF-β to a tumor promoter. However, we found that mp53 does not always promote the oncogenic role of TGF-β. Here, we show that endogenous mp53 knockdown enhanced cell migration and phosphorylation of ERK in DU145 prostate cancer cells. Furthermore, ectopic expression of mp53 in p53-null PC-3 prostate cancer cells enhanced Smad-dependent signaling but inhibited TGF-β-induced cell migration by down-regulating activated ERK. Reactivation of ERK by the expression of its activator, MEK-1, restored TGF-β-induced cell migration. Because TGF-β is known to activate the MAPK/ERK pathway through direct phosphorylation of the adaptor protein ShcA and MAPK/ERK signaling is pivotal to tumor progression, we investigated whether ShcA contributed to mp53-induced ERK inhibition and the conversion of the role of TGF-β during carcinogenesis. We found that mp53 expression led to a decrease of phosphorylated p52ShcA/ERK levels and an increase of phosphorylated Smad levels in a panel of mp53-expressing cancer cell lines and in mammary glands and tumors from mp53 knock-in mice. By manipulating ShcA levels to regulate ERK and Smad signaling in human untransformed and cancer cell lines, we showed that the role of TGF-β in regulating anchorage-dependent and -independent growth and migration can be shifted between growth suppression and migration promotion. Thus, our results for the first time suggest that mp53 disrupts the role of ShcA in balancing the Smad-dependent and -independent signaling activity of TGF-β and that ShcA/ERK signaling is a major pathway regulating the tumor-promoting activity of TGF-β.

Highlights

Biomarkers driving TGF-␤ from tumor-suppressing to tumor-promoting remain elusive
Mutant p53 Inhibits Cell Migration and Down-regulates ERK Signaling in Prostate Cancer Cell Lines—To investigate whether mp53 alone can promote tumor migration, we knocked down mp53 in the human prostate cancer cell line DU145 containing inactivating endogenous p53 P223L and V274F mutations in its DNA-binding domain [37]
Active ERK signaling is reported to be essential for tumor metastasis progression including cell migration [9], suggesting that the mp53 depletion-induced migration was likely caused by the up-regulated ERK signaling

Summary

Background

Biomarkers driving TGF-␤ from tumor-suppressing to tumor-promoting remain elusive. Results: p53 mutation inhibits TGF-␤-induced ShcA/ERK signaling and enhances Smad signaling. By manipulating ShcA levels to regulate ERK and Smad signaling in human untransformed and cancer cell lines, we showed that the role of TGF-␤ in regulating anchoragedependent and -independent growth and migration can be shifted between growth suppression and migration promotion. Our results for the first time suggest that mp disrupts the role of ShcA in balancing the Smad-dependent and -independent signaling activity of TGF-␤ and that ShcA/ERK signaling is a major pathway regulating the tumor-promoting activity of TGF-␤. High levels of TGF-␤ are associated with poor outcome of human cancer [1] It is unclear whether ShcA-mediated activation of ERK signaling contributes to the switch of TGF-␤ function during carcinogenesis. ShcA-mediated ERK signaling appears to play a more dominant role in conferring the tumor-promoting activity of TGF-␤ in the regulation of cell growth and migration. Our finding provides novel insight into the role of ShcA as a promising biomarker in driving TGF-␤ signaling toward tumor promotion

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION