Abstract
Mammalian Ste-20-like Kinases 1 and 2 (MST1/2) are core serine-threonine kinases of the Hippo pathway regulating several cellular processes, including cell cycle arrest and cell death. Here, we discovered a novel alternative splicing variant of the MST2 encoding gene, STK3, in malignant cells and tumor datasets. This variant, named STK3∆7 or MST2∆7 (for mRNA or protein, respectively), resulted from the skipping of exon 7. MST2∆7 exhibited increased ubiquitylation and interaction with the E3 ubiquitin-protein ligase CHIP compared to the full-length protein (MST2FL). Exon 7 in STK3 encodes a segment within the kinase domain, and its exclusion compromised MST2 interaction with and phosphorylation of MOB, a major MST1/2 substrate. Nevertheless, MST2∆7 was capable of interacting with MST1 and MST2FL. Unlike MST2FL, overexpression of MST2∆7 did not lead to increased cell death and growth arrest. Strikingly, we observed the exclusion of STK3 exon 7 in 3.2–15% of tumor samples from patients of several types of cancer, while STK3∆7 was seldomly found in healthy tissues. Our study identified a novel STK3 splicing variant with loss of function and the potential to disturb tissue homeostasis by impacting on MST2 activities in the regulation of cell death and quiescence.
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Data availability
All data related to this study are available in the main figures and supplementary material.
Code availability
Code used for image quantification can be found at https://github.com/brunicardoso/e-signal-lab. Code used for bioinformatics analysis can be made available upon request.
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Acknowledgements
The authors are grateful to Antonio Manucci, Beatriz Moraes, Eduardo Moraes Rego Reis, and Nicolas Hoch for scientific discussions, advice on experiments and insightful inputs. The authors also wish to thank Celia Ludio for technical assistance.
Funding
This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP #2014/10492–0 and #2019/26767–2). RT was initially funded by Instituto Serrapilheira and subsequently by a CAPES postdoctoral fellowship (88882.315500/2019–01). APZPF was a recipient of FAPESP postdoctoral fellowship (#2014/25832–1). AMR was supported by a PhD scholarship from CAPES (88882.332986/2019–01).
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AMR, APZPF, and AB-C conceptualized the work; AMR. APZPF, DS, RT, RJG, AB-C, and MP designed the experiments; PAFG and GADG designed and performed bioinformatics analysis. AMR, APZPF, RT, and AAT performed experiments; AMR, AB-C, and APZPF were responsible for data curation; AB-C and AMR wrote the manuscript; AB-C supervised the work; AB-C, MP, and DS acquired funding to support this work.
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Our research involved human material and human data used in accordance with the Declaration of Helsinki. The RNA samples utilized in the analysis presented in Fig. 5F were extracted from patient samples stored in the Biobank of the São Paulo Cancer Institute Octavio Frias de Oliveira (ICESP). Informed consent was obtained from all subjects. To use these samples, we obtained approval from the National Ethics Committee in Brazil (Comissão Nacional de Ética em Pesquisa; CAAE: 06373719.0.3001.0065).
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Rodrigues, A.M., Paula Zen Petisco Fiore, A., Guardia, G.D.A. et al. Identification of a novel alternative splicing isoform of the Hippo kinase STK3/MST2 with impaired kinase and cell growth suppressing activities. Oncogene (2024). https://doi.org/10.1038/s41388-024-03104-2
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DOI: https://doi.org/10.1038/s41388-024-03104-2