Presenter Status
Student
Abstract Type
Research
Primary Mentor
Tomoo Iwakuma, MD, PhD
Start Date
6-5-2022 11:30 AM
End Date
6-5-2022 1:30 PM
Presentation Type
Poster-Restricted Access
Description
Background: Tumor suppressor p53 (p53) inhibits cancer progression by transactivating genes involved in cell cycle arrest and apoptosis. P53 is mutated in half of all human tumors, which is well correlated with poor patient outcomes. Most of p53 mutations are missense mutations. Missense mutant p53 protein (mutp53) not only loses wild-type p53 (wtp53) transcription factor activity, but also shows oncogenic gain of function that enhances metastasis and drug resistance through protein-protein interactions. However, the exact mechanism by which mutp53 induces drug resistance is poorly described. Moreover, strategies that directly target mutp53 have been challenging.
Objectives/Goal: Our goal is to identify a strategy to specifically target mutp53-expressing tumors in order to minimize the effects of cancer therapy on healthy tissues that do not express mutp53. To achieve this goal, identification of signaling pathways that are specifically altered by mutp53 is essential.
Methods/Design: We initially examined the effects of mutp53 on cancer cell death induced by several common chemotherapy drugs. Multiple mutp53-expressing and -knockdown cell lines were treated with these drugs, followed by trypan-blue exclusion staining and flow cytometry. Drugs that favorably killed mutp53- expressing cells were selected, and the underlying mechanisms were studied.
Results: Consistent with the previous studies, mutp53-expressing cells were less sensitive to common chemotherapy drugs such as cisplatin, etoposide, and doxorubicin. Surprisingly, mutp53-expressing cells were significantly more sensitive to sorafenib (SOR) and vincristine (VCR) than mutp53-knockdown cells. A literature search revealed that both SOR and VCR induce endoplasmic reticulum (ER) stress and ER stress-mediated stress granule (SG) formation. SGs are pro-survival cytoplasmic aggregates of mRNAs and proteins that form as a result of inhibited translation initiation following stress. We hypothesized that mutp53 inhibits pro-survival SG formation through direct interactions with key SGassociated protein(s), thereby sensitizing to ER stress-inducing chemotherapy drugs. Indeed, mutp53 inhibited SG formation induced by ER stress. Moreover, mutp53 bound to the ER-resident eIF2a kinase PERK and thereby inhibited the phosphorylation of eIF2a, a crucial step required for inhibition of translation initiation. Mutp53 also bound the key SG-nucleating factor, G3BP1, but not other SG core proteins, to inhibit recruitment of G3BP1 to the SG. Because SOR is used as a single-agent chemotherapy in hepatocellular carcinoma (HCC), we generated HCC xenografts expressing or lacking mutp53 in immunocompromised mice, followed by treatment with SOR. Consistently, HCC xenografts expressing mutp53 responded better to SOR than tumors lacking mutp53. Mutp53-expressing tumors showed much less SG formation than mutp53-lacking tumors. To support our findings, A TCGA database analysis found that when stratified by p53 mutation status, patients with HCC expressing missense mutp53 had better overall survival than those expressing non-missense mutp53 (p53 null or truncated mutp53).
Conclusions: These results suggest that inhibition of ER stress-mediated SG formation is a novel vulnerability imposed by mutp53, that can be exploited for chemotherapy. FDA-approved chemotherapy drugs that induce ER stress-mediated SGs include SOR and VCR. These drugs may be repurposed to target mutp53-expressing tumors which are otherwise resistant to cancer therapies.
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Additional Files
Targeting stress granule inhibition as a novel vulnerability of mutant p53.pdf (193 kB)Abstract
Targeting stress granule inhibition as a novel vulnerability of mutant p53
Background: Tumor suppressor p53 (p53) inhibits cancer progression by transactivating genes involved in cell cycle arrest and apoptosis. P53 is mutated in half of all human tumors, which is well correlated with poor patient outcomes. Most of p53 mutations are missense mutations. Missense mutant p53 protein (mutp53) not only loses wild-type p53 (wtp53) transcription factor activity, but also shows oncogenic gain of function that enhances metastasis and drug resistance through protein-protein interactions. However, the exact mechanism by which mutp53 induces drug resistance is poorly described. Moreover, strategies that directly target mutp53 have been challenging.
Objectives/Goal: Our goal is to identify a strategy to specifically target mutp53-expressing tumors in order to minimize the effects of cancer therapy on healthy tissues that do not express mutp53. To achieve this goal, identification of signaling pathways that are specifically altered by mutp53 is essential.
Methods/Design: We initially examined the effects of mutp53 on cancer cell death induced by several common chemotherapy drugs. Multiple mutp53-expressing and -knockdown cell lines were treated with these drugs, followed by trypan-blue exclusion staining and flow cytometry. Drugs that favorably killed mutp53- expressing cells were selected, and the underlying mechanisms were studied.
Results: Consistent with the previous studies, mutp53-expressing cells were less sensitive to common chemotherapy drugs such as cisplatin, etoposide, and doxorubicin. Surprisingly, mutp53-expressing cells were significantly more sensitive to sorafenib (SOR) and vincristine (VCR) than mutp53-knockdown cells. A literature search revealed that both SOR and VCR induce endoplasmic reticulum (ER) stress and ER stress-mediated stress granule (SG) formation. SGs are pro-survival cytoplasmic aggregates of mRNAs and proteins that form as a result of inhibited translation initiation following stress. We hypothesized that mutp53 inhibits pro-survival SG formation through direct interactions with key SGassociated protein(s), thereby sensitizing to ER stress-inducing chemotherapy drugs. Indeed, mutp53 inhibited SG formation induced by ER stress. Moreover, mutp53 bound to the ER-resident eIF2a kinase PERK and thereby inhibited the phosphorylation of eIF2a, a crucial step required for inhibition of translation initiation. Mutp53 also bound the key SG-nucleating factor, G3BP1, but not other SG core proteins, to inhibit recruitment of G3BP1 to the SG. Because SOR is used as a single-agent chemotherapy in hepatocellular carcinoma (HCC), we generated HCC xenografts expressing or lacking mutp53 in immunocompromised mice, followed by treatment with SOR. Consistently, HCC xenografts expressing mutp53 responded better to SOR than tumors lacking mutp53. Mutp53-expressing tumors showed much less SG formation than mutp53-lacking tumors. To support our findings, A TCGA database analysis found that when stratified by p53 mutation status, patients with HCC expressing missense mutp53 had better overall survival than those expressing non-missense mutp53 (p53 null or truncated mutp53).
Conclusions: These results suggest that inhibition of ER stress-mediated SG formation is a novel vulnerability imposed by mutp53, that can be exploited for chemotherapy. FDA-approved chemotherapy drugs that induce ER stress-mediated SGs include SOR and VCR. These drugs may be repurposed to target mutp53-expressing tumors which are otherwise resistant to cancer therapies.
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