Regulation of PRMT5–MDM4 axis is critical in the response to CDK4/6 inhibitors in melanoma

Abstract

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are an established treatment in estrogen receptor-positive breast cancer and are currently in clinical development in melanoma, a tumor that exhibits high rates of CDK4 activation. We analyzed melanoma cells with acquired resistance to the CDK4/6 inhibitor palbociclib and demonstrate that the activity of PRMT5, a protein arginine methyltransferase and indirect target of CDK4, is essential for CDK4/6 inhibitor sensitivity. By indirectly suppressing PRMT5 activity, palbociclib alters the pre-mRNA splicing of MDM4, a negative regulator of p53, leading to decreased MDM4 protein expression and subsequent p53 activation. In turn, p53 induces p21, leading to inhibition of CDK2, the main kinase substituting for CDK4/6 and a key driver of resistance to palbociclib. Loss of the ability of palbociclib to regulate the PRMT5–MDM4 axis leads to resistance. Importantly, combining palbociclib with the PRMT5 inhibitor GSK3326595 enhances the efficacy of palbociclib in treating naive and resistant models and also delays the emergence of resistance. Our studies have uncovered a mechanism of action of CDK4/6 inhibitors in regulating the MDM4 oncogene and the tumor suppressor, p53. Furthermore, we have established that palbociclib inhibition of the PRMT5–MDM4 axis is essential for robust melanoma cell sensitivity and provide preclinical evidence that coinhibition of CDK4/6 and PRMT5 is an effective and well-tolerated therapeutic strategy. Overall, our data provide a strong rationale for further investigation of novel combinations of CDK4/6 and PRMT5 inhibitors, not only in melanoma but other tumor types, including breast, pancreatic, and esophageal carcinoma.

Hypoxia-Induced Adaptations of miRNomes and Proteomes in Melanoma Cells and Their Secreted Extracellular Vesicles

“…PRMT5 (Protein arginine methyltransferase 5) is upregulated under hypoxia [50] and has many roles in cancer [51]. Recently, PRMT5 was shown to be involved in drug resistance against CDK4/6 inhibitors in melanoma [52]. Using a Cox regression model, we estimated the survival in relation to protein expression and taking tumour stages into account.…”

Advances in cyclin-dependent kinase inhibitors for the treatment of melanoma

“…In addition to enforcing cell arrest (and therefore causing cytostasis), CDK4/6i have been shown to enhance cancer cell immunogenicity in mice [66], modulate MAPK signaling [67] and induce a senescence-like phenotype [68]. CDK4/6i also indirectly target protein arginine methyltransferase 5 (PRMT5), an epigenetic modifier, resulting in reduced expression of the oncogene MDM4 and subsequent p53 activation [69].…”

“…Another potential biomarker of CDKi resistance that has been investigated is a result of the indirect action of CDK4/6i on the PMRT5-MDM4-p53 axis [69]. Studies have suggested that the indirect suppression of PMRT5 by pablociclib is vital for subsequent p53 activation, and the loss of this action could be a measurable driver for Palbociclib resistance [69].…”

“…Another potential biomarker of CDKi resistance that has been investigated is a result of the indirect action of CDK4/6i on the PMRT5-MDM4-p53 axis [69]. Studies have suggested that the indirect suppression of PMRT5 by pablociclib is vital for subsequent p53 activation, and the loss of this action could be a measurable driver for Palbociclib resistance [69]. In addition, work by Romano and colleagues [104] has looked to assess the mechanism of resistance in one patient who initially responded but then progressed within the aforementioned phase 1b ribociclib/binimetinib combination trial.…”

CDK4/6 inhibition in cancer: the cell cycle splicing connection

“…In order to identify mechanisms of acquired resistance to palbociclib in melanoma, we employed multiple high throughput approaches including reverse phase protein arrays, global gene expression analysis and a drug screen. 3 What we uncovered was that in melanoma cells, CDK4/6 inhibitors ultimately led to CDK2 inhibition via a novel signaling pathway ( Figure 1). Specifically, in drug sensitivity cells, palbociclib suppressed protein arginine methyltransferase 5 (PRMT5) activity, a known modulator of pre-mRNA splicing, which resulted in alterations in mouse double minute 4 (MDM4) pre-mRNA splicing and reduced expression of MDM4 protein.…”