Posttranslational regulation of liver kinase B1 (LKB1) in human cancer

The role of STK11/LKB1 in cancer biology: implications for ovarian tumorigenesis and progression

STK11 (serine-threonine kinase 11), also known as LKB1 (liver kinase B1) is a highly conserved master kinase that regulates cellular metabolism and polarity through a complex signaling network involving AMPK and 12 other AMPK-related kinases. Germline mutations in LKB1 have been causatively linked to Peutz-Jeghers Syndrome (PJS), an autosomal dominant hereditary disease with high cancer susceptibility. The identification of inactivating somatic mutations in LKB1 in different types of cancer further supports its tumor suppressive role. Deleterious mutations in LKB1 are frequently observed in patients with epithelial ovarian cancer. However, its inconsistent effects on tumorigenesis and cancer progression suggest that its functional impact is genetic context-dependent, requiring cooperation with other oncogenic lesions. In this review, we summarize the pleiotropic functions of LKB1 and how its altered activity in cancer cells is linked to oncogenic proliferation and growth, metastasis, metabolic reprogramming, genomic instability, and immune modulation. We also review the current mechanistic understandings of this master kinase as well as therapeutic implications with particular focus on the effects of LKB1 deficiency in ovarian cancer pathogenesis. Lastly, we discuss whether LKB1 deficiency can be exploited as an Achilles heel in ovarian cancer.

GSK3β and UCHL3 govern RIPK4 homeostasis via deubiquitination to enhance tumor metastasis in ovarian cancer

Receptor-interacting protein kinase 4 (RIPK4) is increasingly recognized as a pivotal player in ovarian cancer, promoting tumorigenesis and disease progression. Despite its significance, the posttranslational modifications dictating RIPK4 stability in ovarian cancer remain largely uncharted. In this study, we first established that RIPK4 levels are markedly higher in metastatic than in primary ovarian cancer tissues through single-cell sequencing. Subsequently, we identified UCHL3 as a key deubiquitinase that regulates RIPK4. We elucidate the mechanism that UCHL3 interacts with and deubiquitinates RIPK4 at the K469 site, removing the K48-linked ubiquitin chain and thus enhancing RIPK4 stabilization. Intriguingly, inhibition of UCHL3 activity using TCID leads to increased RIPK4 ubiquitination and degradation. Furthermore, we discovered that GSK3β-mediated phosphorylation of RIPK4 at Ser420 enhances its interaction with UCHL3, facilitating further deubiquitination and stabilization. Functionally, RIPK4 was found to drive the proliferation and metastasis of ovarian cancer in a UCHL3-dependent manner both in vitro and in vivo. Importantly, positive correlations between RIPK4 and UCHL3 protein expression levels were observed, with both serving as indicators of poor prognosis in ovarian cancer patients. Overall, this study uncovers a novel pathway wherein GSK3β-induced phosphorylation of RIPK4 strengthens its interaction with UCHL3, leading to increased deubiquitination and stabilization of RIPK4, thereby promoting ovarian cancer metastasis. These findings offer new insights into the molecular underpinnings of ovarian cancer and highlight potential therapeutic targets for enhancing antitumor efficacy.

PyLKB1 regulates glucose transport via activating PyAMPKα in Yesso Scallop Patinopecten yessoensis under high temperature stress

Liver kinase B1 (LKB1) is a classical serine/threonine protein kinase and plays an important role in maintaining energy homeostasis through phosphorylate AMP-activated protein kinase α subunit (AMPKα). In this study, a homologous molecule of LKB1 with a typical serine/threonine kinase domain and two nuclear localization sequences (NLSs) was identified in Yesso Scallop Patinopecten yessoensis (PyLKB1). The mRNA transcripts of PyLKB1 were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in hepatopancreas. PyLKB1 was mainly located in cytoplasm and nucleus of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyLKB1, PyAMPKα, and PyGLUT1 in hepatopancreas, the phosphorylation level of PyAMPKα at Thr170 in hepatopancreas, the positive fluorescence signals of PyLKB1 in haemocytes, glucose analogue 2-NBDG content in haemocytes, and glucose content in hepatopancreas, haemocytes and serum all increased significantly (p < 0.05) compared to blank group (15 °C). However, there was no significant difference at the protein level of PyLKB1 and PyAMPKα. After PyLKB1 was knockdown by siRNA, the mRNA expression level of PyGLUT1, and the glucose content in hepatopancreas and serum were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. However, there were no significant difference in PyGLUT1 expression, glucose content and glucose analogue 2-NBDG content in haemocytes. These results collectively suggested that PyLKB1-PyAMPKα pathway was activated to promote glucose transport by regulating PyGLUT1 in response to high temperature stress. These results would be helpful for understanding the function of PyLKB1-PyAMPKα pathway in regulating glucose metabolism and maintaining energy homeostasis under high temperature stress in scallops.

Atherosclerosis, Diabetes Mellitus, and Cancer: Common Epidemiology, Shared Mechanisms, and Future Management

The involvement of cardiovascular disease in cancer onset and development represents a contemporary interest in basic science. It has been recognized, from the most recent research, that metabolic syndrome-related conditions, ranging from atherosclerosis to diabetes, elicit many pathways regulating lipid metabolism and lipid signaling that are also linked to the same framework of multiple potential mechanisms for inducing cancer. Otherwise, dyslipidemia and endothelial cell dysfunction in atherosclerosis may present common or even interdependent changes, similar to oncogenic molecules elevated in many forms of cancer. However, whether endothelial cell dysfunction in atherosclerotic disease provides signals that promote the pre-clinical onset and proliferation of malignant cells is an issue that requires further understanding, even though more questions are presented with every answer. Here, we highlight the molecular mechanisms that point to a causal link between lipid metabolism and glucose homeostasis in metabolic syndrome-related atherosclerotic disease with the development of cancer. The knowledge of these breakthrough mechanisms may pave the way for the application of new therapeutic targets and for implementing interventions in clinical practice.