Additionally, SHP2 upregulation is also documented in solid tumors like breast, pancreatic, non–small cell lung (NSCLC), and head and neck cancers.3-5 In contrast, certain germline heterozygous mutations decreasing SHP2 activity cause 90% of Noonan Syndrome with Multiple Lentigines (NSML) or LEOPARD Syndrome, a developmental disorder with symptoms of cardiac malfunction, retardation of growth, and abnormalities of the genitals such as undescended testicles.6,7 Though studies prevalently focus on delineating the effect of loss of function SHP2 mutants, neither the signaling outcomes of impaired nuclear phosphatase activity causing human disorder is known, nor are the nuclear targets.
A recent study led by Prof. Nupam Mahajan at Washington University published in Nature Communications identified the existence of a novel epigenetic mark, pY54-H3 (phosphorylation of histones H3 at Tyr54) which is erased by SHP2 suggesting that pY54-H3 is a direct substrate of SHP2 phosphatase activity.8 ACK1, also known as TNK2, is an oncogenic non-receptor tyrosine kinase overexpressed in multiple cancers including prostate, breast, and lung.9-11 Prostate cancer cells with high ACK1 kinase activity, phosphorylated SHP2 (pY580-SHP2) which in turn promoted enhanced pY54-H3 removal. Significantly, treatment with ACK1 inhibitor, (R)-9b, and SHP2 inhibitor, SHP099 reversed the effect prompting the role of ACK1-SHP2 signaling in the regulation of the pY54-H3 epigenetic mark.
Figure 1: SHP2 phosphorylation by ACK1 promotes interaction with AR, followed by nuclear translocation. SHP2 erases pY54-H3 epigenetic marks upregulating AR transcription, a schematic representation.
ChIP sequencing deciphered the pY54-H3 epigenetic footprint, demonstrating that the enhancer and exon of androgen receptor (AR) are some of the regions marked by pY54-H3 deposition. Prostate cancer cells expressing SHP2-Y580F mutant or treated with ACK1 or SHP2 inhibitors confirmed this observation. Coimmunoprecipitation studies confirmed the interaction of ACK1 and AR with SHP2 and further showed that ACK1 promotes pSHP2/AR complex formation and nuclear translocation consequently expunging pY54-H3 epigenetic marks. Treatment of cells with AR antagonists like abiraterone or enzalutamide or cells with mutant AR compromised SHP2’s nuclear translocation that reflected in increased pY54-H3 mark deposition on AR.
Further analysis of the effect of ACK1/SHP2 signaling on AR showed that NCOR1 and NCOR2, the AR corepressors were instrumented in recognizing the pY54-H3 to suppress the transcription of AR. The clinical relevance of this cellular signaling was validated using a tissue microarray of human prostate tumors, which showed a positive correlation of pACK1 and pSHP2 expression with progression of prostate cancer to metastatic stage, while pY54-H3 levels showed a negative correlation. Additionally, stem cells from NSML patient bearing SHP2 Q510E mutations exhibited a robust increase in global pY54-H3 levels, as well as their increased deposition at the AR gene locus, resulting in a significant decrease in AR mRNA and protein expression.
Overall, this study presents a previously unknown direct chromatin-modifying role of protein tyrosine phosphatases, SHP2 that erased pY54-H3 repressive marks upon phosphorylation by ACK1, leading to AR transcriptional activation (Figure 1). Although existence of this signaling nexus is demonstrated in clinical conditions like prostate cancer and NSML, we expect this mechanism could be associated with the pathogenesis of other tyrosine phosphatase-associated human diseases and cancers. The pACK1/pSHP2/pY54-H3/AR signaling opens the use of previously untested therapeutic modalities and will expand the clinical application of ACK1 small molecule inhibitor, (R)-9b to treat certain human disorders as well as multiple cancers, including castration-resistant prostate cancer (CRPC). A clinical trial of (R)-9b is expected to be initiated in early 2025 for prostate cancer patients.
Funding Support: NIH/NCI grants (1R01CA273054 and 1R01CA276502) and Department of Defense grant (W81XWH-21-1-0202).
Written by: Dhivya Sridaran1,2 and Nupam Mahajan1,2,3
- Department of Surgery, Washington University at St Louis, MO
- Division of Urologic Surgery, Washington University at St Louis, MO
- Siteman Cancer Center, Washington University at St Louis, MO
- Neel, B. G., Gu, H. & Pao, L. The ‘Shp'ing news: SH2 domain-containing tyrosine phosphatases in cell signaling. Trends in biochemical sciences 28, 284-293 (2003).
- Bentires-Alj, M. et al. Activating mutations of the noonan syndrome-associated SHP2/PTPN11 gene in human solid tumors and adult acute myelogenous leukemia. Cancer research 64, 8816-8820 (2004).
- Chan, G., Kalaitzidis, D. & Neel, B. G. The tyrosine phosphatase Shp2 (PTPN11) in cancer. Cancer and metastasis reviews 27, 179-192 (2008).
- Mohi, M. G. & Neel, B. G. The role of Shp2 (PTPN11) in cancer. Current opinion in genetics & development 17, 23-30 (2007).
- Ruess, D. A. et al. Mutant KRAS-driven cancers depend on PTPN11/SHP2 phosphatase. Nature medicine 24, 954-960 (2018).
- Legius, E. et al. PTPN11 mutations in LEOPARD syndrome. Journal of medical genetics 39, 571-574 (2002).
- Kontaridis, M. I., Swanson, K. D., David, F. S., Barford, D. & Neel, B. G. PTPN11 (Shp2) mutations in LEOPARD syndrome have dominant negative, not activating, effects. Journal of Biological Chemistry 281, 6785-6792 (2006).
- Chouhan, S. et al. SHP2 as a primordial epigenetic enzyme expunges histone H3 pTyr-54 to amend androgen receptor homeostasis. Nat Commun 15, 5629, doi:10.1038/s41467-024-49978-4 (2024).
- Mahajan, K. & Mahajan, N. P. ACK1/TNK2 tyrosine kinase: molecular signaling and evolving role in cancers. Oncogene 34, 4162-4167 (2015).
- Mahajan, K. et al. ACK1/TNK2 regulates histone H4 Tyr88-phosphorylation and AR gene expression in castration-resistant prostate cancer. Cancer cell 31, 790-803. e798 (2017).
- Sawant, M. et al. Epigenetic reprogramming of cell cycle genes by ACK1 promotes breast cancer resistance to CDK4/6 inhibitor. Oncogene 42, 2263-2277, doi:10.1038/s41388-023-02747-x (2023).