Research sheds light on the role of PTPRK in tissue repair and cancer

Key points:

• Research from the Sharpe lab at the Institute has advanced our knowledge of multiple roles for PTPRK, a receptor tyrosine phosphatase linked to the regulation of cell-cell adhesion, growth factor signalling and tumour suppression.
• Through a characterisation of the function of PTPRK in human cell lines and mice, the team distinguished catalytic and non-catalytic functions of PTPRK.
• The findings extend what is known about the signalling mechanisms involving PTPRK as a phosphatase and its role in colorectal health but also shed new light on the extent of its function via non-catalytic signalling mechanisms.

Receptor protein tyrosine phosphatases are cell membrane-localised proteins. They are regulators of cell-cell contacts and are also considered likely to be tumour suppressors but the specifics of how they function are unknown. A member of this family, PTPRK, is implicated as a tumour suppressor in several cancer types, particularly colorectal cancer, and mutations and genetic events inactivating PTPRK are found in human colorectal cancers. PTPRK has also been linked genetically to celiac disease.

The Sharpe lab at the Institute investigated the role and signalling mechanisms of PTPRK in cell adhesion, growth factor signalling and tumour suppression in the mouse colon and also in human colorectal cancer cells. Their findings, published in the Journal of Cell Science, are relevant to better understanding the cellular environments that function to repress tumour development as well as understanding the cell interactions that affect repair after injury and potentially cancer metastasis.

Dr Katie Young, lead author on the paper who undertook this research as a PhD student in the Sharpe lab, said: “Through this work we aimed to investigate the role of PTPRK in the colon, working together several observations in the field and connecting these back to the complex signalling mechanisms behind them. It’s vital that we know more about how receptor protein tyrosine phosphatases sense and transmit signals to ensure the healthy growth of our cells, as well as how errors in these mechanisms cause disease.”

Using human colorectal cancer cell lines, the team found that the deletion of PTPRK altered the appearance of the cells, compared to control cells where PTPRK was functional, and observed that the knockout cells showed impaired wound-healing response, which was likely to be due to the loss of PTPRK affecting coordinated action by cells and their neighbours and defects in cellular polarisation.

Utilising a mouse line where PTPRK had been deleted, the team uncovered a role for PTPRK in colon repair. When inflammation of the colon (colitis) was stimulated, mice lacking PTPRK showed a more severe response, demonstrating either increased susceptibility to damage or decreased repair following inflammation. The knockout mice also developed larger and more invasive tumours in a colorectal cancer model compared to wild-type controls, confirming that PTPRK has a role in suppressing tumour growth and invasion.

Using a catalytic mutant, where the catalytic function of PTPRK was abolished, and a xenograft model where cancer cells were transplanted into mice, the researchers confirmed the function for PTPRK in suppressing tumour growth and demonstrated that this was independent of the protein’s phosphatase activity.

Comparing gene expression profiles between cells with and without PTPRK, the team identified genes that were affected by the loss of PTPRK. These genes are characterised in function as being related to epithelial cell identity (being involved in the epithelial to mesenchymal transition and mesenchymal cell differentiation).

The team hypothesise that PTPRK regulation could be a central factor giving plasticity in epithelial barriers, such as lines the intestines, to facilitate epithelial repair while providing a signal to stop the repair response.

Analysing the xenograft tumour samples, the team quantified tyrosine phosphorylation to determine the signalling mechanisms by which PTPRK suppresses tumour development. Their work suggests that the suppression of epidermal growth factor receptor (EGFR) signalling by PTPRK is a key factor and is mediated separately from its function as a phosphatase.

Dr Hayley Sharpe, group leader in the Signalling research programme at the Institute, said: “The goal of our research was to pull several observations together and begin to fill in the gaps of what we don’t know about PTPRK. It has been assumed that PTPs act as tumour suppressors by countering kinase activity by dephosphorylation on oncogenic phosphotyrosine modifications. Therefore, the non-catalytic role of PTPRK in signalling is really intriguing to us and how it achieves this is an important next question to fully understand its role in tumour suppression.”

Notes to Editors

Publication reference
Young et al. (2024). The receptor protein tyrosine phosphatase PTPRK promotes intestinal repair and catalysis-independent tumor suppression. Journal of Cell Science

Press contact
Dr Louisa Wood, Head of Communications, louisa.wood@babraham.ac.uk

Affiliated authors (in author order):
Katie Young, former PhD student in the Sharpe lab
Kasia Wojdyla, postdoc, Sharpe lab
Tiffany Lai, PhD student, Sharpe lab
Katie Mulholland, postdoc, Sharpe lab
Silvia Aldaz Casanova, lab manager, Sharpe lab
Simon Andrews, Head of Bioinformatics
Laura Biggins, bioinformatician, Bioinformatics group
Gareth Fearnley, former postdoc, Sharpe lab
Hayley Sharpe, Group leader, Signalling programme

Image description: Immunofluorescent images of mouse colons stained for nuclei (DAPI;blue) and tight junctions (ZO1; green)

Research funding
This research was supported by the following funding:

• a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society awarded to Hayley Sharpe.
• a BBSRC institutional programme grant and core capability grant to the Institute.
• Katie Young was supported by a CRUK PhD studentship.
• Tiffany Lai is funded by a PhD jointly funded by Trinity College, Cambridge, and the BBSRC Cambridge SBS-DTP.

Animal research statement
As a publicly funded research institute, the Babraham Institute is committed to engagement and transparency in all aspects of its research. The research presented here used surrogate mice to bear PTPRK knock-out mice. The resulting genetically engineered PTPRK knockout and wild type (genetically unaltered) mice were used in procedures to induce colitis (inflammation in the colon) and to monitor the progression of introduced colorectal tumours. Humane endpoints and welfare scoring (such as monitoring weight loss, inactivity, posture and grooming) were defined as part of the study approval and implemented in the experiments. Nude mice were used in the analysis of tumour xenografts (transplantation under the skin of mice) with body weight and tumour diameter measured three times per week. Mice were humanely killed once the tumour reached 12 mm in mean diameter.

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