Par3 regulates invasion of pancreatic cancer cells via interaction with Tiam1

Cell polarity proteins promote macropinocytosis in response to metabolic stress

Macropinocytosis has emerged as a nutrient-scavenging pathway that cancer cells exploit to survive the nutrient-deprived conditions of the tumor microenvironment. Cancer cells are especially reliant on glutamine for their survival, and in pancreatic ductal adenocarcinoma (PDAC) cells, glutamine deficiency can enhance the stimulation of macropinocytosis, allowing the cells to escape metabolic stress through the production of extracellular-protein-derived amino acids. Here, we identify the atypical protein kinase C (aPKC) enzymes, PKCζ and PKCι as novel regulators of macropinocytosis. In normal epithelial cells, aPKCs are known to regulate cell polarity in association with the scaffold proteins Par3 and Par6, controlling the function of several targets, including the Par1 kinases. In PDAC cells, we identify that each of these cell polarity proteins are required for glutamine stress-induced macropinocytosis. Mechanistically, we find that the aPKCs are regulated by EGFR signaling or by the transcription factor CREM to promote the relocation of Par3 to microtubules, facilitating macropinocytosis in a dynein-dependent manner. Importantly, we determine that cell fitness impairment caused by aPKC depletion is rescued by the restoration of macropinocytosis and that aPKCs support PDAC growth in vivo. These results identify a previously unappreciated role for cell polarity proteins in the regulation of macropinocytosis and provide a better understanding of the mechanistic underpinnings that control macropinocytic uptake in the context of metabolic stress.

Loss of polarity protein Par3 in the intestinal epithelium promotes colitis-associated colorectal cancer progression by damaging tight junction assembly

Partitioning defective 3 (Par3) is a polarity protein critical in establishing epithelial cell polarity and tight junctions (TJs). Impaired intestinal epithelial barrier integrity is closely associated with colitis-associated colorectal cancer (CRC) progression. According to the GEO and TCGA database analyses, we first observed that the expression of Par3 was reduced in CRC patients. To understand how Par3 is related to CRC, we investigated the role of Par3 in the development of CRC using an in vivo genetic approach. Our results show that the intestinal epithelium-specific PAR3 deletion mice demonstrated a more severe CRC phenotype in the context of azoxymethane/dextran sodium sulfate (AOM/DSS) treatment, with a corresponding increase in tumor number and inflammatory cytokines profile. Mechanistically, loss of Par3 disrupts the TJs of the intestinal epithelium and increases mucosal barrier permeability. The interaction of Par3 with ZO-1 prevents intramolecular interactions within ZO-1 protein and facilitates the binding of occludin to ZO-1, hence preserving TJs integrity. Our results suggest that Par3 deficiency permits pathogenic bacteria and their endotoxins to penetrate the intestinal submucosa and activate TLR4/MyD88/NF-κB signaling, promoting inflammation-driven CRC development and that Par3 may be a novel potential molecular marker for the diagnosis of early-stage CRC.

Dual Function of Par3 in Tumorigenesis

Cell maintenance and the establishment of cell polarity involve complicated interactions among multiple protein complexes as well as the regulation of different signaling pathways. As an important cell polarity protein, Par3 is evolutionarily conserved and involved in tight junction formation as well as tumorigenesis. In this review, we aimed to explore the function of Par3 in tumorigenesis. Research has shown that Par3 exhibits dual functions in human cancers, both tumor-promoting and tumor-suppressive. Here, we focus on the activities of Par3 in different stages and types of tumors, aiming to offer a new perspective on the molecular mechanisms that regulate the functions of Par3 in tumor development. Tumor origin, tumor microenvironment, tumor type, cell density, cell–cell contact, and the synergistic effect of Par3 and other tumor-associated signaling pathways may be important reasons for the dual function of Par3. The important role of Par3 in mammalian tumorigenesis and potential signaling pathways is context dependent.

The polarity protein PARD3 and cancer

Tissue disorganisation is one of the main hallmarks of cancer. Polarity proteins are responsible for the arrangement of cells within epithelial tissues through the asymmetric organisation of cellular components. Partition defective 3 (PARD3) is a master regulator of the Par polarity complex primarily due to its ability to form large complexes via its self-homologous binding domain. In addition to its role in polarity, PARD3 is a scaffolding protein that binds to intracellular signalling molecules, many of which are frequently deregulated in cancer. The role of PARD3 has been implicated in multiple solid cancers as either a tumour suppressor or promoter. This dual functionality is both physiologically and cell context dependent. In this review, we will discuss PARD3's role in tumourigenesis in both laboratory and clinical settings. We will also review several of the mechanisms underpinning PARD3's function including its association with intracellular signalling pathways and its role in the regulation of asymmetric cell division.

High expression of PARD3 predicts poor prognosis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most commonly cancers with poor prognosis and drug response. Identifying accurate therapeutic targets would facilitate precision treatment and prolong survival for HCC. In this study, we analyzed liver hepatocellular carcinoma (LIHC) RNA sequencing (RNA-seq) data from The Cancer Genome Atlas (TCGA), and identified PARD3 as one of the most significantly differentially expressed genes (DEGs). Then, we investigated the relationship between PARD3 and outcomes of HCC, and assessed predictive capacity. Moreover, we performed functional enrichment and immune infiltration analysis to evaluate functional networks related to PARD3 in HCC and explore its role in tumor immunity. PARD3 expression levels in 371 HCC tissues were dramatically higher than those in 50 paired adjacent liver tissues (p < 0.001). High PARD3 expression was associated with poor clinicopathologic feathers, such as advanced pathologic stage (p = 0.002), vascular invasion (p = 0.012) and TP53 mutation (p = 0.009). Elevated PARD3 expression also correlated with lower overall survival (OS, HR = 2.08, 95% CI = 1.45-2.98, p < 0.001) and disease-specific survival (DSS, HR = 2.00, 95% CI = 1.27-3.16, p = 0.003). 242 up-regulated and 71 down-regulated genes showed significant association with PARD3 expression, which were involved in genomic instability, response to metal ions, and metabolisms. PARD3 is involved in diverse immune infiltration levels in HCC, especially negatively related to dendritic cells (DCs), cytotoxic cells, and plasmacytoid dendritic cells (pDCs). Altogether, PARD3 could be a potential prognostic biomarker and therapeutic target of HCC.

Par3/integrin β1 regulates embryo adhesion via changing endometrial luminal epithelium polarity†

The objective is to investigate the pathophysiological significance of Par3 and integrin β1 with regard to the functionality of the endometrial luminal epithelium (LE). Design: laboratory study; setting: university research laboratory. Analysis involved endometrial aspirates and endometrial adenocarcinoma cells (HEC-1A) and endometrial carcinoma cells (RL95-2). We first examined the expression and localization of Par3 and integrin β1 in HEC-1A cells and RL95-2 cells. Then we knocked down Par3 and integrin β1 in HEC-1A cells and RL95-2 cells, respectively, and found that Par3/integrin β1 affected embryo adhesion by regulating the intercellular tight junctions' (TJs') structure and thus the polarity of the endometrial LE. These findings were also confirmed in the endometrium specimens from human and mice. The main outcome measures were the expression and localization of Par3 and integrin β1 in the endometrial epithelial cell lines and endometrium specimens and the regulations of Par3 and integrin β1 on TJs, polarity, and embryo adhesion. Following the knockdown of Par3 in HEC-1A cells, there was a reduction in the complexity of the TJs and cell polarity, and the adhered blastocysts number was significantly increased. However, the reduction of integrin β1 in RL95-2 cells resulted in effects that directly opposed those following the knockdown of Par3 in HEC-1A cells. Estrogen and progesterone reduced the expression of Par3 and promoted the expression of integrin β1 in HEC-1A cells. Par3/integrin β1 regulates embryo adhesion by regulating intercellular TJs' structure and polarity of endometrial LE under the action of ovarian hormones.

RAS-mediated suppression of PAR3 and its effects on SCC initiation and tissue architecture occur independently of hyperplasia

Proper epithelial development and homeostasis depends on strict control of oriented cell division. Current evidence shows that this process is regulated by intrinsic polarity factors and external spatial cues. Owing to the lack of an appropriate model system that can recapitulate the architecture of the skin, deregulation of spindle orientation in human epithelial carcinoma has never been investigated. Here, using an inducible model of human squamous cell carcinoma (SCC), we demonstrate that RAS-dependent suppression of PAR3 (encoded by PARD3) accelerates epithelial disorganization during early tumorigenesis. Diminished PAR3 led to loss of E-cadherin-mediated cell adhesion, which in turn contributed to misoriented cell division. Pharmacological inhibition of the MAPK pathway downstream of RAS activation reversed the defects in PAR3 expression, E-cadherin-mediated cell adhesion and mitotic spindle orientation. Thus, temporal analysis of human neoplasia provides a powerful approach to study cellular and molecular transformations during early oncogenesis, which allowed identification of PAR3 as a critical regulator of tissue architecture during initial human SCC development.

Cigarette smoking promotes cancer-related transformation of oral epithelial cells through activation of Wnt and MAPK pathway

Aim: Study aims to investigate the effect of cigarette smoking on cancer-related transformation in oral epithelial cells of smokers through evaluating the alteration in Wnt/β-catenin and MAPK pathways. Materials & methods: Exfoliated oral epithelial cells were collected from 138 subjects and categorized into nonsmokers, smokers and clinically diagnosed precancer and cancer patients. Real-time quantitative PCR was performed to detect the fold changes of related genes. Expressions of biomarkers were assessed using immunofluorescence and western blot. Results: Study shows significant (p < 0.001) alteration in mRNA level of TNF-α, NF-κβ, FZD1, β-catenin, PARD 3, MAPK1 and vimentin genes under cigarette smoking. Conclusion: Results suggested the progression of oral cancer under cigarette smoking occurs through multiple events and activation of canonical Wnt/MAPK pathways.

Pard3 suppresses glioma invasion by regulating RhoA through atypical protein kinase C/NF-κB signaling

Partitioning defective protein 3 (Pard3) has been reported to inhibit the progression of numerous human cancer cell types. However, the role of Pard3 in glioma progression remains unclear. In this study, the expression of Pard3 was measured in human gliomas of different grades by both quantitative polymerase chain reaction and Western blotting. The effect of Pard3 on glioma progression was tested using cell counting kit‐8 assays, EdU assays, colony formation assays, cell migration, and invasion assays and tumor xenografts. The effect of Pard3 on Ras homolog family member A (RhoA) protein levels, subcellular localization, and transcriptional activity was measured by immunoblotting and immunofluorescence. Our results indicate that Pard3 functions as a tumor suppressor in gliomas and that the loss of Pard3 protein is strongly associated with a higher grade and poorer outcome. Pard3 overexpression inhibits glioma progression by upregulating RhoA protein levels. However, the level of GTP‐RhoA protein remained unchanged. Further evidence demonstrates that Pard3 regulates RhoA protein levels, subcellular localization and transcriptional activity by activating atypical protein kinase C/NF‐κB signaling. Mouse modeling experiments show that Pard3 overexpression inhibits glioma cell growth in vivo. Taken together, these findings identify RhoA as a novel target of Pard3 in gliomas and substantiate a novel regulatory role for Pard3 in glioma progression. This study reveals that Pard3 plays an inhibitory role in gliomas by regulating RhoA, which reveals a potential benefit for Pard3 activators in the prevention and therapy of gliomas.

MicroRNA 483-3p targets Pard3 to potentiate TGF-β1-induced cell migration, invasion, and epithelial-mesenchymal transition in anaplastic thyroid cancer cells

Anaplastic thyroid cancer (ATC) is associated with poor prognosis and is often untreatable. MicroRNA 483-3p (miR-483) and partitioning-defective 3 (Pard3), a member of the Pard family, have functions and regulatory mechanisms in ATC. The abnormal regulation of miR-483 may play an important role in tumorigenesis, and Par3 is known to regulate cell polarity, cell migration, and cell division. Tumor proliferation promoted by the regulation of miRNA expression can be regulated in thyroid cancer by upregulating transforming growth factor-β1 (TGF-β1), which is thought to interact with Pard3. When compared with adjacent non-tumor tissues, we found that miR-483 was upregulated and Pard3 was downregulated in 80 thyroid tumor samples. Disease-free survival was decreased when expression of miR-483 was upregulated and Pard3 expression was downregulated. Cell growth, migration, and invasion were induced by overexpression of miR-483. However, knockdown of miR-483 resulted in a loss of cell invasion and viability, both in vitro and in vivo. The expression of Pard3 was increased by the inhibition of miR-483, but TGF-β1-induced cell migration and invasion were decreased by miR-483 inhibition. A dual-luciferase reporter assay determined that Pard3 expression was downregulated when targeted with miR-483. The epithelial–mesenchymal transition (EMT), as well as Tiam1-Rac signaling, was induced by TGF-β1, which was decreased by the overexpression of Pard3. Pard3 decreased the inhibition of EMT and Tiam-Rac1 signaling, which resulted from transfection of ATC cells with miR-483. Overall, the results showed that downregulation of Pard3 resulted in increased cell invasion and EMT in ATC, which was promoted by treatment with miR-483. These findings suggest novel therapeutic targets and treatment strategies for this disease.

Regulation of spermatid polarity by the actin- and microtubule (MT)-based cytoskeletons

It is conceivable that spermatid apico-basal polarity and spermatid planar cell polarity (PCP) are utmost important to support spermatogenesis. The orderly arrangement of developing germ cells in particular spermatids during spermiogenesis are essential to obtain structural and nutrient supports from the fixed number of Sertoli cells across the limited space of seminiferous epithelium in the tubules following Sertoli cell differentiation by ∼17 day postpartum (dpp) in rodents and ∼12 years of age at puberty in humans. Yet few studies are found in the literature to investigate the role of these proteins to support spermatogenesis. Herein, we briefly summarize recent findings in the field, in particular emerging evidence that supports the concept that apico-basal polarity and PCP are conferred by the corresponding polarity proteins through their effects on the actin- and microtubule (MT)-based cytoskeletons. While much research is needed to bridge our gaps of understanding cell polarity, cytoskeletal function, and signaling proteins, a critical evaluation of some latest findings as summarized herein provides some important and also thought-provoking concepts to design better functional experiments to address this important, yet largely expored, research topic.

Loss of TDP43 inhibits progression of triple-negative breast cancer in coordination with SRSF3

Aberrant alternative splicing has been highlighted as a potential hallmark of cancer. Here, we identify TDP43 (TAR DNA-binding protein 43) as an important splicing regulator responsible for the unique splicing profile in triple-negative breast cancer (TNBC). Clinical data demonstrate that TDP43 is highly expressed in TNBC with poor prognosis. Knockdown of TDP43 inhibits tumor progression, including proliferation and metastasis, and overexpression of TDP43 promotes proliferation and malignancy of mammary epithelial cells. Deep sequencing analysis and functional experiments indicate that TDP43 alters most splicing events with splicing factor SRSF3 (serine/arginine-rich splicing factor 3), in the regulation of TNBC progression. The TDP43/SRSF3 complex controls specific splicing events, including downstream genes PAR3 and NUMB The effect of reduced metastasis and proliferation upon the knockdown of TDP43 or SRSF3 is mediated by the splicing regulation of PAR3 and NUMB exon 12, respectively. The TDP43/SRSF3 complex and downstream PAR3 isoform are potential therapeutic targets for TNBC.

High expression of partitioning defective 3-like protein is associated with malignancy in colorectal cancer

Partitioning defective 3-like protein is a novel cell polarity protein. Recently, partitioning defective 3-like protein has been demonstrated with tumor-promoting function by disrupting tight junction, inhibiting tumor suppressor liver kinase B1, and maintaining mammary stem cells. For the first time, we studied partitioning defective 3-like protein expression in malignant colorectal cancer. We used immunohistochemistry scoring system to evaluate partitioning defective 3-like protein expression in 196 colorectal cancer tissues and 33 adjacent normal tissues. We found that colorectal cancer tissues had much stronger partitioning defective 3-like protein immunoreactivity than normal tissues, and colorectal cancer patients with positive partitioning defective 3-like protein expression were characterized with higher cancer stages, metastasis, poor tumor differentiation, larger tumor size, as well as high levels of colorectal cancer markers carcinoembryonic antigen and cancer antigen 19-9. Besides, partitioning defective 3-like protein overexpression was independently predictive of lower survival rate in colorectal cancer patients, even after adjusting the influence of cofactors. Moreover, we also found that partitioning defective 3-like protein was associated with rapid growing colorectal cancer, while knockdown of partitioning defective 3-like protein expression largely inhibited cancer cell proliferation. Our study provided the first evidence that partitioning defective 3-like protein was overexpressed in colorectal cancer and associated with disease malignancy. Also, partitioning defective 3-like protein may serve as a promising prognostic marker and a potential therapeutic target for colorectal cancer treatment. Further study is necessary to understand the regulatory mechanism of partitioning defective 3-like protein in colorectal cancer and the feasibility of its application in clinic.

Choline, Other Methyl-Donors and Epigenetics

Choline dietary intake varies such that many people do not achieve adequate intakes. Diet intake of choline can modulate methylation because, via betaine homocysteine methyltransferase (BHMT), this nutrient (and its metabolite, betaine) regulate the concentrations of S-adenosylhomocysteine and S-adenosylmethionine. Some of the epigenetic mechanisms that modify gene expression without modifying the genetic code depend on the methylation of DNA or of histones; and diet availability of choline and other methyl-group donors influences both of these methylations. Examples of methyl-donor mediated epigenetic effects include the changes in coat color and body weight in offspring when pregnant agouti mice are fed high choline, high methyl diets; the changes in tail kinking in offspring when pregnant Axin(Fu) mice are fed high choline, high methyl diets; the changes in Cdkn3 methylation and altered brain development that occurs in offspring when pregnant rodents are fed low choline diets. When choline metabolism is disrupted by deleting the gene Bhmt, DNA methylation is affected (especially in a region of chromosome 13), expression of specific genes is suppressed, and liver cancers develop. Better understanding of how nutrients such as choline and methyl-donors influence epigenetic programs has importance for our understanding of not only developmental abnormalities but also for understanding the origins of chronic diseases.

Altered methylation of specific DNA loci in the liver of Bhmt-null mice results in repression of Iqgap2 and F2rl2 and is associated with development of preneoplastic foci

Folate B₁₂-dependent remethylation of homocysteine is important, but less is understood about the importance of the alternative betaine-dependent methylation pathway-catalyzed by betaine-homocysteine methyltransferase (BHMT)-for establishing and maintaining adequate DNA methylation across the genome. We studied C57Bl/6J Bhmt (betaine-homocysteine methyltransferase)-null mice at age 4, 12, 24, and 52 wk (N = 8) and observed elevation of S-adenosylhomocysteine concentrations and development of preneoplastic foci in the liver (increased placental glutathione S-transferase and cytokeratin 8-18 activity; starting at 12 wk). At 4 wk, we identified 63 differentially methylated CpGs (DMCs; false discovery rate < 5%) proximal to 81 genes (across 14 chromosomes), of which 18 were differentially expressed. Of these DMCs, 52% were located in one 15.5-Mb locus on chromosome 13, which encompassed the Bhmt gene and defined a potentially sensitive region with mostly decreased methylation. Analyzing Hybrid Mouse Diversity Panel data, which consisted of 100 inbred strains of mice, we identified 97 DMCs that were affected by Bhmt genetic variation in the same region, with 7 overlapping those found in Bhmt-null mice (P < 0.001). At all time points, we found a hypomethylated region mapping to Iqgap2 (IQ motif-containing GTPase activating protein 2) and F2rl2 (proteinase-activated receptor-3), 2 genes that were also silenced and underexpressed, respectively.-Lupu, D. S., Orozco, L. D., Wang, Y., Cullen, J. M., Pellegrini, M., Zeisel, S. H. Altered methylation of specific DNA loci in the liver of Bhmt-null mice results in repression of Iqgap2 and F2rl2 and is associated with development of preneoplastic foci.

Claudin proteins, outside-in signaling, and carcinogenesis

Environment affects an individual's development and disease risk which then suggest that the environmental cues must have ways of reaching to the cellular nuclei to orchestrate desired genetic changes. Polarized and differentiated epithelial cells join together by cell-cell adhesions to create a protective sheet which separates body's internal milieu from its environment, albeit in highly regulated manner. Among these cell-cell adhesions, a key role of tight junction, the apical cell-cell adhesion, in maintaining epithelial cell polarity and differentiation is well recognized. Moreover, significant changes in expression and cellular distribution of claudin proteins, integral component of the tight junction, characterize pathophysiological changes including neoplastic growth and progression. Studies have further confirmed existence of complex claudin-based interactomes and demonstrated that changes in such protein partnering can influence barrier integrity and communication between a cell and its environment to produce undesired outcome. Cell signaling is the process by which cells respond to their environment to make dynamic decisions to live, grow and proliferate, or die. Thus, pivotal role of the deregulated tight junction structure/function in influencing cellular signaling cascades to alter cellular phenotype can be envisaged, however, is not well understood. Needless to mention that advanced knowledge in this area can help improve therapeutic considerations and preventive measures. Here, we discuss potential role of the tight junction in the regulation of "outside-in" signaling to regulate cancer growth, with specific focus upon the claudin family of proteins.