PKMYT1 Promotes Epithelial-Mesenchymal Transition Process in Triple-Negative Breast Cancer by Activating Notch Signaling.

Background: Triple-negative breast cancer (TNBC) is a subtype of breast cancer (BC) that lacks receptors for targeted therapy. Deeper insight into the molecular mechanisms regulating TNBC metastasis is urgently needed. The epithelial-mesenchymal transition process facilitates the metastasis of neighboring epithelial tumor cells. Protein kinase, membrane-associated tyrosine/threonine 1 (PKMYT1), a member of the Wee family of protein kinases, is upregulated in BC, and its high expression predicts poor prognosis in BC patients. Notch signaling activation is a pathognomonic feature of TNBC. PKMYT1 has been found to induce EMT in non-small cell lung cancer by activating Notch signaling. However, whether PKMYT1 exerts effects on TNBC progression by regulating Notch signaling remains unknown.

Objectives: The objective of this study was to investigate whether PKMYT1 exerts effects on TNBC progression by regulating Notch signaling.

Methods: Fifty cases of surgically resected BC samples (tumor and adjacent non-tumor tissue samples) were collected from patients diagnosed with BC. We measured the expression of PKMYT1 in clinical samples with real-time quantitative polymerase chain reaction (RT-qPCR). For in vitro analysis, RT-qPCR and Western blotting were conducted to evaluate PKMYT1 expression in TNBC cells. Then, the viability, migration, and invasion of TNBC cells were detected by cell counting kit-8 assays, wound healing assays, and Transwell assays. The EMT event was examined by evaluating the levels of EMT-associated proteins. For in vivo analysis, xenograft models in nude mice were established to explore PKMYT1 roles. E-cadherin and Ki67 expression in xenograft models were estimated by immunohistochemistry staining. Hematoxylin and eosin staining was performed to assess tumor metastasis. The underlying mechanisms by which PKMYT1 affected the malignant phenotypes of TNBC cells were explored by Western blotting measuring the pathway-associated proteins.

Results: PKMYT1 was upregulated in BC tissues and cells, and its knockdown prevented cell proliferation, migration, invasion, and EMT event in TNBC. Mechanistically, Notch signaling was inactivated by PKMYT1 depletion, and Notch activation abolished the PKMYT1 silencing-induced inhibition in the malignant phenotypes of TNBC cells. For in vivo analysis, PKMYT1 knockdown inhibited tumorigenesis and metastasis of TNBC.

Conclusion: PKMYT1 promotes EMT, proliferation, migration, and invasion of TNBC cells and facilitates tumor growth and metastasis by activating Notch signaling.