Abstract
Activated α2-macroglobulin (α2M*) signals predominantly through cell surface GRP78 (CS-GRP78) to promote proliferation and survival of cancer cells; however, the molecular mechanism remains obscure. c-MYC is an essential transcriptional regulator that controls cell proliferation. We hypothesize that α2M*/CS-GRP78-evoked key signaling events are required for transcriptional activation of c-MYC target genes. Activation of CS-GRP78 by α2M* requires ligation of the GRP78 primary amino acid sequence (Leu(98)-Leu(115)). After stimulation with α2M*, CS-GRP78 signaling activates 3-phosphoinositide-dependent protein kinase-1 (PDK1) to induce phosphorylation of PLK1, which in turn induces c-MYC transcription. We demonstrate that PLK1 binds directly to c-MYC and promotes its transcriptional activity by phosphorylating Ser(62) Moreover, activated c-MYC is recruited to the E-boxes of target genes FOSL1 and ID2 by phosphorylating histone H3 at Ser(10) In addition, targeting the carboxyl-terminal domain of CS-GRP78 with a mAb suppresses transcriptional activation of c-MYC target genes and impairs cell proliferation. This work demonstrates that α2M*/CS-GRP78 acts as an upstream regulator of the PDK1/PLK1 signaling axis to modulate c-MYC transcription and its target genes, suggesting a therapeutic strategy for targeting c-MYC-associated malignant progression.
Highlights
In the development of metastatic prostate cancer (2, 9, 16 –19)
We demonstrated that ␣2M*/CSGRP78 signaling is required for mechanistic target of rapamycin complex-mediated phosphorylation of Akt by 3-phosphoinositide-dependent protein kinase-1 (PDK1) [22]
On the basis of biochemical and functional evidence, we show that ␣2M*/CS-GRP78-dependent PDK1/PLK1 signaling is required for the transcriptional activation of a subset of c-MYC target genes and cell proliferation
Summary
Cell Culture—1-LN prostate cancer cells were a kind gift from Dr Philip Walther, Department of Surgery, Duke University Medical Center. They reside in our laboratory and are available on request. 1-LN and DU145 cells were maintained in RPMI 1640 medium (Sigma) containing 10% fetal bovine serum (FBS), 1% penicillin/streptomycin at 37 °C in a 5% CO2-humidified atmosphere. A375 and U373 cells were maintained in DMEM (high glucose; Gibco, Life Technologies) containing 10% FBS, 1% penicillin/streptomycin at 37 °C in a 5% CO2-humidified atmosphere. Shc-MYC lentiviral particles (Clone ID TRCN000000-39642) were obtained from Sigma and transfected into 1-LN cells according to the manufacturer’s instructions.
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