SIK2 maintains breast cancer stemness by phosphorylating LRP6 and activating Wnt/β-catenin signaling

Role of the Wnt signaling pathway in the complex microenvironment of breast cancer and prospects for therapeutic potential (Review)

The focus on breast cancer treatment has shifted from the cytotoxic effects of single drugs on tumor cells to multidimensional multi‑pathway synergistic intervention strategies targeting the tumor microenvironment (TME). The activation of the Wnt signaling pathway in the TME of breast cancer cells serves a key regulatory role in tissue homeostasis and is a key driver of the carcinogenic process. Modulating the crosstalk between the Wnt pathway and TME of breast cancer is key for understanding the biological behavior of breast cancer and advancing the development of novel antitumor drugs. The present review aimed to summarize the complex mechanisms of the Wnt signaling pathway in the breast cancer TME, interactions between the Wnt signaling pathway and components of the breast cancer TME and breast cancer‑associated genes, as well as the interactions between the Wnt signaling pathway and other signaling cascades at the molecular level. Furthermore, the present review aimed to highlight the unique advantages of the Wnt signaling pathway in the macro‑regulation of the TME and the current therapeutic strategies targeting the Wnt signaling pathway, their potential clinical value and future research directions in breast cancer treatment.

Salt-inducible kinase 2 confers radioresistance in colorectal cancer by facilitating homologous recombination repair

Resistance to radiotherapy remains a critical barrier in treating colorectal cancer (CRC), particularly in cases of locally advanced rectal cancer (LARC). To identify key kinases involved in CRC radioresistance, we employed a kinase-targeted CRISPR-Cas9 library screen. This approach aimed to identify potential kinase inhibitors as radiosensitizers. Our screening identified salt-inducible kinase 2 (SIK2) as a critical factor in CRC radioresistance. Increased SIK2 expression correlated with reduced tumor regression and poorer outcomes in LARC patients undergoing neoadjuvant chemoradiotherapy. The depletion of SIK2 significantly enhanced radiation-induced apoptosis and tumor regression. Mechanistically, SIK2 interacts with valosin-containing protein (VCP), promoting its hyperphosphorylation. This modification improves VCP's capacity to extract K48-linked ubiquitin-conjugated proteins from chromatin, thus aiding the recruitment of RPA and RAD51 to DNA damage sites. This mechanism strengthens homologous recombination-mediated DNA repair, which contributes to radioresistance. Importantly, ARN-3236, a SIK2 inhibitor, markedly sensitized CRC cells to radiation both in vivo and in vitro, providing a potential strategy to overcome radioresistance. In summary, our findings reveal a novel mechanism by which SIK2 contributes to the radioresistance of CRC, proposing SIK2 as a potential therapeutic target with its inhibitor significantly enhancing CRC radiotherapy efficacy.

LRP11 facilitates lipid metabolism and malignancy in hepatocellular carcinoma by stabilizing RACK1 through USP5 regulation

Hepatocellular carcinoma (HCC) is one of the most prevalent cancers worldwide and a major public health challenge. Lipid metabolism plays a crucial role in the metabolic reprogramming observed in HCC, although the underlying mechanisms are still being elucidated. Nile red staining and lipid assays showed that LRP11 knockdown significantly reduces lipid accumulation in HCC cells, with a concurrent decrease in key lipid metabolism markers such as FSAN, ACLY and ACSL4, as demonstrated by Western blotting. Mass spectrometry (MS) and co-immunoprecipitation (Co-IP) revealed that LRP11 recruits USP5, enhancing USP5-mediated deubiquitination of RACK1. Truncation analysis identified LRP11 residues 309-500 as critical for interaction with the RACK1 residues 91-231. These findings suggest that LRP11 may influence lipid metabolism and progression in HCC through USP5-mediated stabilization of RACK1. Based on these results, LRP11 emerges as a potential target for further exploration in HCC therapy. Targeting LRP11 or disrupting its interactions with USP5 or RACK1 could offer new avenues for treatment, though additional research is required to validate these therapeutic possibilities.

Salt-inducible kinases (SIKs) in cancer: mechanisms of action and therapeutic prospects

Salt-inducible kinases (SIKs), a group of serine/threonine kinases in the adenosine monophosphate-activated protein kinase (AMPK) family, exist in three isoforms: SIK1, SIK2 and SIK3. These kinases are crucial in various physiological processes. Emerging evidence indicates that dysregulation of SIK expression and activation significantly contributes to carcinogenesis by promoting cellular proliferation, metabolic dysregulation, metastasis and chemoresistance through the modulation of crucial signaling pathways. The role of SIKs in cancer progression and metastasis involves complex mechanisms that vary among cancer types. Additionally, research on SIK inhibitors suggests that targeting these kinases might offer promising avenues for improving cancer treatment outcomes.

Exosomal miR-502-5p suppresses the progression of gastric cancer by repressing angiogenesis through the Wnt/β-catenin pathway

BACKGROUND

Gastric cancer (GC) is a significant global health concern, ranking as the fifth most common cancer and the third leading cause of cancer-related deaths. The role of miR-502-5p in various cancers has been studied, but its specific impact on gastric cancer through exosomes is not well understood. This study aimed to investigate the role and mechanism of exosome-derived miR-502-5p in gastric cancer.

METHODS

Differential expression of miR-502-5p in tissues or serum of GC patients was determined using qRT-PCR. The impact of miR-502-5p on cell proliferation, migration, and invasion was assessed through in vitro and in vivo experiments. The potential of exosome-miR-502-5p to inhibit metastatic ability was also explored by using vivo and vitro assay. Furthermore, the underlying mechanism of miR-502-5p in gastric cancer was investigated using western blotting.

RESULTS

It was found that miR-502-5p suppressed the proliferation, migration, and invasion of gastric cancer cells. Exosome-miR-502-5p expression was negatively linked to metastatic ability and demonstrated inhibition of metastasis in vitro and in vivo. Additionally, miR-502-5p appeared to inhibit angiogenesis through the Wnt/β-catenin pathway in gastric cancer.

CONCLUSIONS

Exosomal miR-502-5p acts as a suppressor in the development and progression of gastric cancer, suggesting its potential as a target for anti-cancer therapy or as a diagnostic biomarker.

Belling the "cat": Wnt/β-catenin signaling and its significance in future cancer therapies

The WNT/β-catenin is among one of the most extensively studied cellular signaling pathways involved in the initiation and progression of several deadly cancers. It is now understood that the WNT/β-catenin signaling, during tumor progression operates in a very complex fashion beyond the earlier assumed simple WNT 'On' or 'Off' mode as it recruits numerous WNT ligands, receptors, transcriptional factors and also cross-talks with other signaling molecules including the noncanonical WNT regulators. WNT/β-catenin signaling molecules are often mutated in different cancers which makes them very challenging to inhibit and sometimes ranks them among the undruggable targets. Furthermore, due to the evolutionary conservation of this pathway, inhibiting WNT/β-catenin has caused significant toxicity in normal cells. These challenges are reflected in clinical trial data, where the use of WNT/β-catenin inhibitors as standalone treatments remains limited. In this review, we have highlighted the crucial functional associations of diverse WNT/β-catenin signaling regulators with cancer progression and the phenotypic switching of tumor cells. Next, we have shed light on the roles of WNT/β-catenin signaling in drug resistance, clonal evolution, tumor heterogeneity, and immune evasion. The present review also focuses on various classes of routine and novel WNT/β-catenin therapeutic regimes while addressing the challenges associated with targeting the regulators of this complex pathway. In the light of multiple case studies on WNT/β-catenin inhibitors, we also highlighted the challenges and opportunities for future clinical trial strategies involving these treatments. Additionally, we have proposed strategies for future WNT/β-catenin-based drug discovery trials, emphasizing the potential of combination therapies and AI/ML-driven prediction approaches. Overall, here we showcased the opportunities, possibilities, and potentialities of WNT/β-catenin signaling modulatory therapeutic regimes as promising precision cancer medicines for the future.

Post-translational modifications: The potential ways for killing cancer stem cells

While strides in cancer treatment continue to advance, the enduring challenges posed by cancer metastasis and recurrence persist as formidable contributors to the elevated mortality rates observed in cancer patients. Among the multifaceted factors implicated in tumor recurrence and metastasis, cancer stem cells (CSCs) emerge as noteworthy entities due to their inherent resistance to conventional therapies and heightened invasive capacities. Characterized by their notable abilities for self-renewal, differentiation, and initiation of tumorigenesis, the eradication of CSCs emerges as a paramount objective. Recent investigations increasingly emphasize the pivotal role of post-translational protein modifications (PTMs) in governing the self-renewal and replication capabilities of CSCs. This review accentuates the critical significance of several prevalent PTMs and the intricate interplay of PTM crosstalk in regulating CSC behavior. Furthermore, it posits that the manipulation of PTMs may offer a novel avenue for targeting and eliminating CSC populations, presenting a compelling perspective on cancer therapeutics with substantial potential for future applications.

A novel SIK2 inhibitor SIC-19 exhibits synthetic lethality with PARP inhibitors in ovarian cancer

PURPOSE

Ovarian cancer patients with HR proficiency (HRP) have had limited benefits from PARP inhibitor treatment, highlighting the need for improved therapeutic strategies. In this study, we developed a novel SIK2 inhibitor, SIC-19, and investigated its potential to enhance the sensitivity and expand the clinical utility of PARP inhibitors in ovarian cancer.

METHODS

The SIK2 protein was modeled using a Molecular Operating Environment (MOE), and the most favorable model was selected based on a GBVI/WSA dG scoring function. The Chembridge Compound Library was screened, and the top 20 candidate compounds were tested for their interaction with SIK2 and downstream substrates, AKT-pS473 and MYLK-pS343. SIC-19 emerged as the most promising drug candidate and was further evaluated using multiple assays.

RESULTS

SIC-19 exhibited selective and potent inhibition of SIK2, leading to its degradation through the ubiquitination pathway. The IC50 of SIC-19 correlated inversely with endogenous SIK2 expression in ovarian cancer cell lines. Treatment with SIC-19 significantly inhibited cancer cell growth and sensitized cells to PARP inhibitors in vitro, as well as in ovarian cancer organoids and xenograft models. Mechanistically, SIK2 knockdown and SIC-19 treatment reduced RAD50 phosphorylation at Ser635, prevented nuclear translocation of RAD50, disrupted nuclear filament assembly, and impaired DNA homologous recombination repair, ultimately inducing apoptosis. These findings highlight the crucial role of SIK2 in the DNA HR repair pathway and demonstrate the significant PARP inhibitor sensitization achieved by SIC-19 in ovarian cancer.

CONCLUSIONS

SIC-19, a novel SIK2 inhibitor, effectively inhibits tumor cell growth in ovarian cancer by interfering with RAD50-mediated DNA HR repair. Furthermore, SIC-19 enhances the efficacy of PARP inhibitors, providing a promising therapeutic strategy to improve outcomes for ovarian cancer patients.

Breast cancer stem cells generate immune-suppressive T regulatory cells by secreting TGFβ to evade immune-elimination

Cancer stem cells (CSCs), being the primary contributors in tumor initiation, metastasis, and relapse, ought to have seminal roles in evasion of immune surveillance. Tumor-promoting CD4+CD25+FOXP3+ T-regulatory cells (Tregs) have been described to abolish host defense mechanisms by impeding the activities of other immune cells including effector T cells. However, whether CSCs can convert effector T cells to immune-suppressive Treg subset, and if yes, the mechanism underlying CSC-induced Treg generation, are limitedly studied. In this regard, we observed a positive correlation between breast CSC and Treg signature markers in both in-silico and immunohistochemical analyses. Mirroring the conditions during tumor initiation, low number of CSCs could successfully generate CD4+CD25+FOXP3+ Treg cells from infiltrating CD4+ T lymphocytes in a contact-independent manner. Suppressing the proliferation potential as well as IFNγ production capacity of effector T cells, these Treg cells might be inhibiting antitumor immunity, thereby hindering immune-elimination of CSCs during tumor initiation. Furthermore, unlike non-stem cancer cells (NSCCs), CSCs escaped doxorubicin-induced apoptosis, thus constituting major surviving population after three rounds of chemotherapy. These drug-survived CSCs were also able to generate CD4+CD25+FOXP3+ Treg cells. Our search for the underlying mechanism further unveiled the role of CSC-shed immune-suppressive cytokine TGFβ, which was further increased by chemotherapy, in generating tumor Treg cells. In conclusion, during initiation as well as after chemotherapy, when NSCCs are not present in the tumor microenvironment, CSCs, albeit present in low numbers, generate immunosuppressive CD4+CD25+FOXP3+ Treg cells in a contact-independent manner by shedding high levels of immune-suppressive Treg-polarizing cytokine TGFβ, thus escaping immune-elimination and initiating the tumor or causing tumor relapse.

The AMPK-like protein kinases Sik2 and Sik3 interact with Hipk and induce synergistic tumorigenesis in a Drosophila cancer model

Homeodomain-interacting protein kinases (Hipks) regulate cell proliferation, apoptosis, and tissue development. Overexpression of Hipk in Drosophila causes tumorigenic phenotypes in larval imaginal discs. We find that depletion of Salt-inducible kinases Sik2 or Sik3 can suppress Hipk-induced overgrowth. Furthermore, co-expression of constitutively active forms of Sik2 or Sik3 with Hipk caused significant tissue hyperplasia and tissue distortion, indicating that both Sik2 and Sik3 can synergize with Hipk to promote tumorous phenotypes, accompanied by elevated dMyc, Armadillo/β-catenin, and the Yorkie target gene expanded. Larvae expressing these hyperplastic growths also display an extended larval phase, characteristic of other Drosophila tumour models. Examination of total protein levels from fly tissues showed that Hipk proteins were reduced when Siks were depleted through RNAi, suggesting that Siks may regulate Hipk protein stability and/or activity. Conversely, expression of constitutively active Siks with Hipk leads to increased Hipk protein levels. Furthermore, Hipk can interact with Sik2 and Sik3 by co-immunoprecipitation. Co-expression of both proteins leads to a mobility shift of Hipk protein, suggesting it is post-translationally modified. In summary, our research demonstrates a novel function of Siks in synergizing with Hipk to promote tumour growth.

Signaling pathways governing the maintenance of breast cancer stem cells and their therapeutic implications

Breast cancer stem cells (BCSCs) represent a distinct subpopulation of cells with the ability to self-renewal and differentiate into phenotypically diverse tumor cells. The involvement of CSC in treatment resistance and cancer recurrence has been well established. Numerous studies have provided compelling evidence that the self-renewal ability of cancer stem cells is tightly regulated by specific signaling pathways, which exert critical roles to maintain an undifferentiated phenotype and prevent the differentiation of CSCs. Signaling pathways such as Wnt/β-catenin, NF-κB, Notch, Hedgehog, TGF-β, and Hippo have been implicated in the promotion of self-renewal of many normal and cancer stem cells. Given the pivotal role of BCSCs in driving breast cancer aggressiveness, targeting self-renewal signaling pathways holds promise as a viable therapeutic strategy for combating this disease. In this review, we will discuss the main signaling pathways involved in the maintenance of the self-renewal ability of BCSC, while also highlighting current strategies employed to disrupt the signaling molecules associated with stemness.

Biological functions and molecular interactions of Wnt/β-catenin in breast cancer: Revisiting signaling networks

Changes in lifestyle such as physical activity and eating habits have been one of the main reasons for development of various diseases in modern world, especially cancer. However, role of genetic factors in initiation of cancer cannot be ignored and Wnt/β-catenin signaling is such factor that can affect tumor progression. Breast tumor is the most malignant tumor in females and it causes high mortality and morbidity around the world. The survival and prognosis of patients are not still desirable, although there have been advances in introducing new kinds of therapies and diagnosis. The present review provides an update of Wnt/β-catenin function in breast cancer malignancy. The upregulation of Wnt is commonly observed during progression of breast tumor and confirms that tumor cells are dependent on this pathway Wnt/β-catenin induction prevents apoptosis that is of importance for mediating drug resistance. Furthermore, Wnt/β-catenin signaling induces DNA damage repair in ameliorating radio-resistance. Wnt/β-catenin enhances proliferation and metastasis of breast tumor. Wnt/β-catenin induces EMT and elevates MMP expression. Furthermore, Wnt/β-catenin participates in tumor microenvironment remodeling and due to its tumor-promoting factor, drugs for its suppression have been developed. Different kinds of upstream mediators Wnt/β-catenin signaling in breast cancer have been recognized that their targeting is a therapeutic approach. Finally, Wnt/β-catenin can be considered as a biomarker in clinical trials.