Tumor promoting effect of podoplanin-positive fibroblasts is mediated by enhanced RhoA activity

New insights into cancer pathology learned from the dynamics of cancer-associated fibroblasts

Paget's "Seed and Soil" theory, proposed in 1889, emphasizes the importance of the microenvironment where cancer cells grow in metastatic sites. Over a century later, this concept remains a cornerstone in comprehending cancer biology and devising treatment strategies. The "Seed and Soil" theory, which initially explained how cancer spreads to distant organs, now also applies to the tumor microenvironment (TME) within primary tumors. This theory emphasizes the critical interaction between cancer cells ("seeds") and their surrounding environment ("soil") and how this interaction affects both tumor progression within the primary site and at metastatic sites. An important point to note is that the characteristics of the TME are not static but dynamic, undergoing substantial changes during tumor progression and after treatment with therapeutic drugs. Cancer-associated fibroblasts (CAFs), recognized as the principal noncancerous cellular component within the TME, play multifaceted roles in tumor progression including promoting angiogenesis, remodeling the extracellular matrix, and regulating immune responses. In this comprehensive review, we focus on the findings regarding how the dynamics of CAFs contribute to cancer progression and drug sensitivity. Understanding the dynamics of CAFs could provide new insights into cancer pathology and lead to important advancements in cancer research and treatment.

The relationship between cancer associated fibroblasts biomarkers and prognosis of breast cancer: a systematic review and meta-analysis

Background

To elucidate the relationship between cancer-associated fibroblast (CAFs) biomarkers and the prognosis of breast cancer patients for individualized CAFs-targeting treatment.

Methodology

PubMed, Web of Science, Cochrane, and Embase databases were searched for CAFs-related studies of breast cancer patients from their inception to September, 2023. Meta-analysis was performed using R 4.2.2 software. Sensitivity analyses were performed to explore the sources of heterogeneity. Funnel plot and Egger's test were used to assess the publication bias.

Results

Twenty-seven studies including 6,830 patients were selected. Univariate analysis showed that high expression of platelet-derived growth factor receptor-β (PDGFR-β) (P = 0.0055), tissue inhibitor of metalloproteinase-2 (TIMP-2) (P < 0.0001), matrix metalloproteinase (MMP) 9 (P < 0.0001), MMP 11 (P < 0.0001) and MMP 13 (P = 0.0009) in CAFs were correlated with reduced recurrence-free survival (RFS)/disease-free survival (DFS)/metastasis-free survival (MFS)/event-free survival (EFS) respectively. Multivariate analysis showed that high expression of α-smooth muscle actin (α-SMA) (P = 0.0002), podoplanin (PDPN) (P = 0.0008), and PDGFR-β (P = 0.0470) in CAFs was associated with reduced RFS/DFS/MFS/EFS respectively. Furthermore, PDPN and PDGFR-β expression in CAFs of poorly differentiated breast cancer patients were higher than that of patients with relatively better differentiated breast cancer. In addition, there is a positive correlation between the expression of PDPN and human epidermal growth factor receptor-2 (HER-2).

Conclusions

The high expression of α-SMA, PDPN, PDGFR-β in CAFs leads to worse clinical outcomes in breast cancer, indicating their roles as prognostic biomarkers and potential therapeutic targets.

What is new in cancer-associated fibroblast biomarkers?

The tumor microenvironment is one of the important drivers of tumor development. Cancer-associated fibroblasts (CAFs) are a major component of the tumor stroma and actively participate in tumor development, invasion, metastasis, drug resistance, and other biological behaviors. CAFs are a highly heterogeneous group of cells, a reflection of the diversity of their origin, biomarkers, and functions. The diversity of CAF origin determines the complexity of CAF biomarkers, and CAF subpopulations expressing different biomarkers may play contrasting roles in tumor progression. In this review, we provide an overview of these emerging CAF biomarkers and the biological functions that they suggest, which may give a better understanding of the relationship between CAFs and tumor cells and be of great significance for breakthroughs in precision targeted therapy for tumors. Video Abstract.

Roles of Podoplanin in Malignant Progression of Tumor

Podoplanin (PDPN) is a cell-surface mucin-like glycoprotein that plays a critical role in tumor development and normal development of the lung, kidney, and lymphatic vascular systems. PDPN is overexpressed in several tumors and is involved in their malignancy. PDPN induces platelet aggregation through binding to platelet receptor C-type lectin-like receptor 2. Furthermore, PDPN modulates signal transductions that regulate cell proliferation, differentiation, migration, invasion, epithelial-to-mesenchymal transition, and stemness, all of which are crucial for the malignant progression of tumor. In the tumor microenvironment (TME), PDPN expression is upregulated in the tumor stroma, including cancer-associated fibroblasts (CAFs) and immune cells. CAFs play significant roles in the extracellular matrix remodeling and the development of immunosuppressive TME. Additionally, PDPN functions as a co-inhibitory molecule on T cells, indicating its involvement with immune evasion. In this review, we describe the mechanistic basis and diverse roles of PDPN in the malignant progression of tumors and discuss the possibility of the clinical application of PDPN-targeted cancer therapy, including cancer-specific monoclonal antibodies, and chimeric antigen receptor T technologies.

The Role of Podoplanin in Skin Diseases

Podoplanin is a sialomucin-like type I transmembrane receptor glycoprotein that is expressed specifically in lymphatic vessels, sebaceous glands, and hair follicles in normal skin. However, under pathological conditions podoplanin expression is upregulated in various cells, such as keratinocytes, fibroblasts, tumor cells, and inflammatory cells, and plays pivotal roles in different diseases. In psoriasis, podoplanin expression is induced in basal keratinocytes via the JAK-STAT pathway and contributes toward epidermal hyperproliferation. Podoplanin expression on keratinocytes can also promote IL-17 secretion from lymphocytes, promoting chronic inflammation. During wound healing, the podoplanin/CLEC-2 interaction between keratinocytes and platelets regulates re-epithelialization at the wound edge. In skin cancers, podoplanin expresses on tumor cells and promotes their migration and epithelial-mesenchymal transition, thereby accelerating invasion and metastasis. Podoplanin is also expressed in normal peritumoral cells, such as cancer-associated fibroblasts in melanoma and keratinocytes in extramammary Paget's disease, which promote tumor progression and predict aggressive behavior and poor prognosis. This review provides an overview of our current understanding of the mechanisms via which podoplanin mediates these pathological skin conditions.

Cancer-associated fibroblasts and the tumor microenvironment in non-small cell lung cancer

INTRODUCTION

Non-small cell lung cancer (NSCLC) has a markedly poor prognosis as it progresses, and the prognosis is still unsatisfactory even with modern treatments. Cancer is composed of not only cancer cells, but also stroma consisting of various cell types. Cancer-associated fibroblasts (CAFs) are a major component of the stroma and the associated tumor microenvironment (TME). Particularly, CAFs are a critical component in elucidating the biological mechanisms of cancer progression and new therapeutic targets. This article outlines the TME formed by CAFs in NSCLC.

AREAS COVERED

Focusing on the TME in NSCLC, we discuss the mechanisms by which CAFs are involved in cancer progression, drug resistance, and the development of therapies targeting CAFs.

EXPERT OPINION

In the TME, CAFs profoundly contribute to tumor progression by interacting with cancer cells through direct contact or paracrine cytokine signaling. CAFs also interact with various other stromal components to establish a tumor-promoting immunosuppressive microenvironment and remodel the extracellular matrix. Furthermore, these effects are closely associated with drug resistance. Further elucidation of the stromal microenvironment, including CAFs, could prove to be crucial in the treatment of NSCLC.

Characterising cancer-associated fibroblast heterogeneity in non-small cell lung cancer: a systematic review and meta-analysis

Cancer-associated fibroblasts (CAFs) are a key component of the tumour microenvironment with evidence suggesting they represent a heterogeneous population. This study summarises the prognostic role of all proteins characterised in CAFs with immunohistochemistry in non-small cell lung cancer thus far. The functions of these proteins in cellular processes crucial to CAFs are also analysed. Five databases were searched to extract survival outcomes from published studies and statistical techniques, including a novel method, used to capture missing values from the literature. A total of 26 proteins were identified, 21 of which were combined into 7 common cellular processes key to CAFs. Quality assessments for sensitivity analyses were carried out for each study using the REMARK criteria whilst publication bias was assessed using funnel plots. Random effects models consistently identified the expression of podoplanin (Overall Survival (OS)/Disease-specific Survival (DSS), univariate analysis HR 2.25, 95% CIs 1.80-2.82) and α-SMA (OS/DSS, univariate analysis HR 2.11, 95% CIs 1.18-3.77) in CAFs as highly prognostic regardless of outcome measure or analysis method. Moreover, proteins involved in maintaining and generating the CAF phenotype (α-SMA, TGF-β and p-Smad2) proved highly significant after sensitivity analysis (HR 2.74, 95% CIs 1.74-4.33) supporting attempts at targeting this pathway for therapeutic benefit.

Relationship between podoplanin-expressing cancer-associated fibroblasts and the immune microenvironment of early lung squamous cell carcinoma

AIM

Cancer-associated fibroblasts (CAFs) expressing podoplanin (PDPN) harbor a fibrous tumor microenvironment that promotes cancer progression in lung adenocarcinoma. In this study, we investigated whether tumor-promoting PDPN⁺ CAFs contribute to the immunosuppressive microenvironment in lung squamous cell carcinoma (SqCC). M&M: The gene expression profiles of immunosuppressive cytokines were compared using The Cancer Genome Atlas (TCGA) microarray lung SqCC data (n = 484) between a PDPN-high group and a PDPN-low group. Further, using patient-derived CAFs from surgically resected lung SqCC, the PDPN⁺ fraction was sorted and gene and protein expressions were analyzed. Finally, immunohistochemical staining was conducted on 131 surgically resected lung SqCC; CD8⁺ and FOXP3⁺ tumor infiltrating lymphocytes (TILs), and CD204⁺ tumor-associated macrophages (TAMs) were evaluated in cases with PDPN⁺ and PDPN^- CAFs.

RESULTS

Analysis of TCGA database revealed that the PDPN-high group exhibited significantly higher expression of interleukin (IL)-1A, IL-1B, IL-6, IL-10, monocyte chemoattractant protein-1 (CCL2), colony stimulating factor 1 (CSF1), fibroblast growth factor 2 (FGF2), galectin 1 (LGALS1), platelet derived growth factor subunit A (PDGFA), PDGFB, and transforming growth factor-β1 (TGFB1) than those in the PDPN-low group. Among them, it was found that TGFB1 expression was higher in patient-derived PDPN⁺ CAFs. Immunohistochemical analyses revealed that more CD204⁺ TAMs infiltrated the tumor tissues in cases with PDPN⁺ CAFs than in cases with PDPN^- CAFs (P <  0.03), while CD8⁺ and FOXP3⁺ TILs did not. Furthermore, in the same tumor, CD204⁺ TAMs infiltrated more in PDPN⁺ CAF-rich areas (P =  0.005).

CONCLUSION

PDPN⁺ CAFs showed higher expression of TGFB1 and were associated with CD204⁺ TAM infiltration in stage-I lung SqCC, suggesting that PDPN⁺ CAFs were associated with the immunosuppressive tumor microenvironment.

Review of cancer-associated fibroblasts and their microenvironment in post-chemotherapy recurrence

Cancer tissue comprises not only cancer cells, but also several types of non-cancerous cells, such as cancer-associated fibroblasts. These fibroblasts directly and/or indirectly communicate with the cancer cells and other types of stromal cells, to create a specific tumor microenvironment. Cytotoxic chemotherapy plays a central role in treating cancer; however, tumor re-progression (recurrence) is a significant problem for cancer patients. Cytotoxic anticancer drugs act on fibroblasts as well as cancer cells and, after chemotherapy, all surviving cells are in contact with one another in the local environment. Therefore, an understanding of the molecular interactions between surviving cancer cells and fibroblasts is necessary to prevent tumor re-progression and to sustain the effect of cytotoxic agents. After chemotherapy, the number of fibroblasts may increase, some of which are identifiable as tumor-promoting. In this review, we discuss the significance of cancer-associated fibroblasts in tumor re-progression after chemotherapy, and the potential value of targeting them to enhance clinical outcomes.

Expression of Podoplanin in Sinonasal Squamous Cell Carcinoma and Its Clinical Significance

BACKGROUND

It was recently suggested that the upregulation of podoplanin (PDPN) in cancer cells plays a significant role in tumor invasion and metastasis and that it is significantly associated with poor prognosis in oral, cutaneous, and esophageal squamous cell carcinoma. The aim of this study was to investigate the expression pattern of PDPN in sinonasal squamous cell carcinoma (SNSCC) and to evaluate its role as a prognostic factor for survival outcome.

PATIENTS AND METHODS

This study included 59 subjects with SNSCC. We retrospectively collected the clinical features of these patients from medical records and retrieved the associated formalin-fixed, paraffin-embedded tissues for PDPN immunohistochemical staining. Furthermore, PDPN expression was analyzed in relation to the patients' clinicopathological features and prognosis.

RESULTS

We observed positive staining for PDPN in both cancer cells and stromal cancer-associated fibroblasts (CAFs). Positive expression of PDPN in cancer cells of patients with SNSCC was significantly correlated with the primary tumor site (p = 0.009) and local recurrence (p = 0.024). In addition, patients with PDPN-positive cancer cells had significantly lower overall survival (OS) and disease-free survival (DFS) rates than did patients with PDPN-negative cancer cells (both p < 0.05). Multivariate analysis revealed that PDPN expression in cancer cells was an independent prognostic factor for both OS (p = 0.038) and DFS (p = 0.039).

CONCLUSIONS

Our findings demonstrated that PDPN overexpression may be both an independent prognostic biomarker and a therapeutic target in SNSCC.

Expression of Podoplanin in Mammary Cancers in Female Dogs

BACKGROUND/AIM

Mammary neoplasms are very common tumours in female dogs. Cancer-associated fibroblasts (CAFs) play an important role in the oncogenesis process. One of the useful proteins used in the diagnostics of CAFs cells is podoplanin (PDPN). The aim of our study was to assess the expression of PDPN in mammary cancer in female dogs.

MATERIALS AND METHODS

Our study cohort included 61 cancers and 21 adenomas of the mammary tumour in bitches. Expression of podoplanin, Ki-67 and HER2 was determined using the Immunohistochemical (IHC) method. PDPN expression at the mRNA level was determined using real-time PCR.

RESULTS

Expression of PDPN in CAFs was observed in 22.9% of cases of mammary cancers in bitches, with no PDPN expression in adenomas. A positive correlation was found between the expression of PDPN in CAFs and the grade of histological malignancy and expression of Ki-67.

CONCLUSION

PDPN plays a significant role during the process of carcinogenesis of mammary tumours in female dogs.

Cancer associated fibroblast: Mediators of tumorigenesis

It is well accepted that the tumor microenvironment plays a pivotal role in cancer onset, development, and progression. The majority of clinical interventions are designed to target either cancer or stroma cells. These emphases have been directed by one of two prevailing theories in the field, the Somatic Mutation Theory and the Tissue Organization Field Theory, which represent two seemingly opposing concepts. This review proposes that the two theories are mutually inclusive and should be concurrently considered for cancer treatments. Specifically, this review discusses the dynamic and reciprocal processes between stromal cells and extracellular matrices, using pancreatic cancer as an example, to demonstrate the inclusivity of the theories. Furthermore, this review highlights the functions of cancer associated fibroblasts, which represent the major stromal cell type, as important mediators of the known cancer hallmarks that the two theories attempt to explain.

PDPN Is Expressed in Various Types of Canine Tumors and Its Silencing Induces Apoptosis and Cell Cycle Arrest in Canine Malignant Melanoma

Podoplanin (PDPN), a small transmembrane mucin-like glycoprotein, is ectopically expressed. It is also known to be linked with several aspects of tumor malignancy in some types of human tumors, including invasion, metastasis, and cancer stemness. However, there are few reports on the expression of dog PDPN (dPDPN) in canine tumors, and the association between dPDPN and tumor malignancy has not been elucidated. We identified that 11 out of 18 types of canine tumors expressed dPDPN. Furthermore, 80% of canine malignant melanoma (MM), squamous cell carcinoma, and meningioma expressed dPDPN. Moreover, the expression density of dPDPN was positively associated with the expression of the Ki67 proliferation marker. The silencing of dPDPN by siRNAs resulted in the suppression of cell migration, invasion, stem cell-like characteristics, and cell viability in canine MM cell lines. The suppression of cell viability was caused by the induction of apoptosis and G2/M phase cell cycle arrest. Overall, this study demonstrates that dPDPN is expressed in various types of canine tumors and that dPDPN silencing suppresses cell viability through apoptosis and cell cycle arrest, thus providing a novel biological role for PDPN in tumor progression.

Organoid culture containing cancer cells and stromal cells reveals that podoplanin-positive cancer-associated fibroblasts enhance proliferation of lung cancer cells

OBJECTIVE

Podoplanin-positive cancer-associated fibroblasts (CAFs) play an important role in tumor progression. The aim of this study was to evaluate the effect of podoplanin (+) CAFs on the proliferation of cancer cells using a three-dimensional (3D) organoid model.

MATERIALS AND METHODS

We examined the success rate of organoid culture containing PC-9 cancer cells and CAFs. Thereafter, we compared the proliferating index (MIB-1 index) of PC-9 cells co-cultured with podoplanin-overexpressing CAFs and control CAFs using organoid specimens. Furthermore, we compared the MIB-1 labeling index of cancer cells in podoplanin (+) CAFs cases (n = 13) and podoplanin (-) CAFs cases (n = 14) using surgically resected adenocarcinoma specimens.

RESULTS

Without CAFs, PC-9 cells did not form any organoid (success rate: 0%). When PC-9 cells were mixed with CAFs (1:10), the mixed cells generated round and steric aggregates (hybrid cancer organoids, success rate: 100%). In three independent experiments, the MIB-1 index of PC-9 cells in hybrid cancer organoids containing podoplanin-overexpressing CAFs was significantly higher than that of PC-9 cells in organoids containing control CAFs (Exp. 1: 40.4% vs. 24.4%; Exp. 2: 40.0% vs. 24.5%; Exp. 3: 40.3% vs. 25.2%; p < 0.001). Surgically resected human tumors revealed that the MIB-1 index of adenocarcinoma cells was significantly higher in the case of podoplanin (+) CAFs than in the case of podoplanin (-) CAFs (34.8% vs. 16.2%; p < 0.01).

CONCLUSION

Our data suggested that the hybrid cancer organoid model might reflect the growth-promoting effect of podoplanin (+) CAFs in cancer cells, and this new system can be a useful tool for evaluating the tumor microenvironment.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Link between tumor-promoting fibrous microenvironment and an immunosuppressive microenvironment in stage I lung adenocarcinoma

OBJECTIVES

Podoplanin-positive cancer-associated fibroblasts [PDPN (+) CAFs] play an important role in cancer progression in non-small-cell lung cancer. The aim of this study was to clarify the correlation between a fibrous microenvironment containing PDPN (+) CAFs and an immune microenvironment.

MATERIALS AND METHODS

A total of 174 patients with pathological stage I lung adenocarcinoma were analyzed. We evaluated PDPN (+) CAFs and immune-related cells, CD 204-positive tumor-associated macrophages [CD204 (+) TAMs], CD8-positive T cells, and FOXP3-positive T cells, in cancer stroma by using immunohistochemical staining. We compared the expression levels of immune-regulatory cytokines between the PDPN high and low expression groups by analyzing the gene expression profiles of lung adenocarcinoma (n = 442).

RESULTS

Presence of PDPN (+) CAFs was a risk factor for recurrence (P =  0.042). The number of CD204 (+) TAMs was significantly higher (P <  0.001) and the CD8/FOXP3 T cell ratio was significantly lower in PDPN (+) CAFs cases than in PDPN (-) CAFs cases (P =  0.027). Within the same tumor, the number of CD 204 (+) TAMs was significantly higher (P <  0.001) and CD8/FOXP3 T cell ratio tended to be lower (P =  0.062) in PDPN (+) CAF areas. Microarray analysis revealed that the PDPN expression-high group had significantly higher gene expression levels of cytokines that inducing M2 macrophage polarization and suppressing immune-related lymphocytes.

CONCLUSION

The current results show that lung adenocarcinoma with PDPN (+) CAFs is typified by the immunosuppressive microenvironment, suggesting a close link between the tumor-promoting fibrous microenvironment and the immunosuppressive microenvironment.

Podoplanin-positive cancer-associated fibroblasts predict poor prognosis in lung cancer patients

Background

Cancer-associated fibroblasts (CAFs) are a heterogeneous population, and different subpopulations play differential roles in tumor microenvironment. However, the prognostic role of podoplanin-positive CAFs in human lung cancer still remains controversial.

Methods

Herein, we performed a meta-analysis including 12 published studies with 1,802 patients identified from PubMed and EBSCO to assess the prognostic impact of podoplanin-positive CAFs in lung cancer patients.

Results

We found that podoplanin⁺ fibroblast infiltration significantly decreased overall survival (OS), disease-free survival (DFS), and progression-free survival in patients. In stratified analyses, podoplanin⁺ fibroblast infiltration was significantly associated with worse OS and DFS in both squamous cell carcinoma and adenocarcinoma of lung. In addition, high density of podoplanin-positive CAFs significantly correlated with unfavorable clinicopathological features such as lymph node metastasis, and lymphatic, vascular, and pleural invasion of patients.

Conclusion

Podoplanin⁺ fibroblast infiltration leads to worse clinical outcome in lung cancer patients, implicating that it is a valuable prognostic biomarker and targeting it may have a potential for effective treatment.

Activated Tumor-infiltrating Fibroblasts Predict Worse Prognosis in Breast Cancer Patients

Purpose: Activated tumor-infiltrating fibroblasts were significantly associated with survival of cancer patients. However, they are heterogeneous population, and the prognostic role of these cells in human breast cancer still remains controversial. Herein, we performed the meta-analysis to better understand the role of these cells in prognosis prediction for breast cancer patients.

Methods: We searched PubMed and EBSCO to identify the studies evaluating the association of intratumoral activated fibroblast density detected by immunohistochemical (IHC) method and overall survival (OS) and/or disease-free survival (DFS) in breast cancer patients, then computed extracted data into hazard ratios (HRs) for OS, DFS and clinicopathological features such as lymph node metastasis, TNM stage with STATA 12.0.

Results: A total of 3680 patients with breast cancer from 15 published studies were incorporated into this meta-analysis. We found that the infiltration of activated fibroblasts significantly decreased overall survival (OS) and disease-free survival (DFS) in patients. In stratified analyses, high density of FSP-1⁺ or podoplanin⁺ fibroblasts was significantly associated with worse OS; while α-SMA⁺ or podoplanin⁺ fibroblast infiltration was associated with worse DFS in breast cancer. In addition, elevated number of activated tumor-infiltrating fibroblasts significantly correlated with lymph node metastasis and poor tumor differentiation of patients.

Conclusion: The infiltration of activated fibroblasts, especially the FSP-1⁺ or podoplanin⁺ fibroblasts leads to worse clinical outcome in breast cancer patients, implicating that it is a valuable prognostic biomarker and targeting it may have a potential for effective treatment.

LpMab-23-recognizing cancer-type podoplanin is a novel predictor for a poor prognosis of early stage tongue cancer

Purpose

We report that the reactivity of a novel monoclonal antibody LpMab-23 for human cancer-type podoplanin (PDPN) is a predictor for a poor prognosis of tongue cancer.

Patients and Methods

The association between LpMab-23-recognizing cancer-type PDPN expression and clinical/pathological features were analyzed on 60 patients with stage I and II tongue cancer treated with transoral resection of the primary tumor.

Results

In the mode of invasion, the LpMab-23-dull/negative cases were significantly larger in cases with low-grade malignancies and without late cervical lymph node metastasis, than in cases with high-grade malignancies and the metastasis. In the high-grade malignant cases, LpMab-23-positive cases were significantly larger than LpMab-23-dull/negative cases. The Kaplan–Meier curves of the five-year metastasis-free survival rate (MFS) were significantly lower in the LpMab-23 positive patients than in LpMab-23 dull/negative patients. The LpMab-23-dull/negative cases showed the highest MFS in all of the clinical/pathological features and particularly, the MFS of the LpMab-23 positive cases decreased to less than 60% in the first year. In the Cox proportional hazard regression models a comparison of the numbers of LpMab-23 dull/negative with positive cases showed the highest hazard ratio with statistical significance in all of the clinical/pathological features.

Conclusions

LpMab-23 positive cases may be considered to present a useful predictor of poor prognosis for early stage tongue cancer.

Podoplanin emerges as a functionally relevant oral cancer biomarker and therapeutic target

Oral cancer has become one of the most aggressive types of cancer, killing 140,000 people worldwide every year. Current treatments for oral cancer include surgery and radiation therapies. These procedures can be very effective; however, they can also drastically decrease the quality of life for survivors. New chemotherapeutic treatments are needed to more effectively combat oral cancer. The transmembrane receptor podoplanin (PDPN) has emerged as a functionally relevant oral cancer biomarker and chemotherapeutic target. PDPN expression promotes tumor cell migration leading to oral cancer invasion and metastasis. Here, we describe the role of PDPN in oral squamous cell carcinoma progression, and how it may be exploited to prevent and treat oral cancer.

Abundant tumor promoting stromal cells in lung adenocarcinoma with hypoxic regions

OBJECTIVES

Carbonic anhydrase IX (CAIX) is a marker of hypoxia and its expression by cancer associated fibroblasts (CAFs) was reportedly associated with the poor prognosis of lung adenocarcinoma. This study aimed to characterize the hypoxic microenvironment containing CAIX (+) CAFs.

MATERIALS AND METHODS

First, we evaluated the clinicopathological significance of CAIX expression by CAFs in 3cm and above lung adenocarcinoma (n=188). We then compared the expressions of E-cadherin, ezrin, ALDH-1, CD44, EGFR, HSF-1, Glut-1, and PD-L1 in cancer cells, as well as those of CD204 and podoplanin in stromal cells between CAIX (+) CAFs and CAIX (-) CAFs cases (n=25, each).

RESULTS

In total, 48 patients had CAIX (+) CAFs (26%). Multivariate analysis revealed that CAIX expression by CAFs could serve as an independent unfavorable prognostic factor for recurrence-free survival (p<0.05). The staining score of hypoxia marker Glut-1 in cancer cells was significantly higher in cases with CAIX (+) CAFs than in those with CAIX (-) CAFs (median: 20 vs. 0, p<0.01). In addition, the numbers of CD204 (+) tumor-associated macrophages (TAMs) and podoplanin (+) CAFs were significantly higher in the CAIX (+) CAFs group than in the CAIX (-) CAFs group (TAMs: 31.5 vs. 17.0: p<0.01, CAFs: 20 vs. 0: p<0.05). The staining score of the other markers did not differ between the groups.

CONCLUSION

Our results indicate that the presence of abundant tumor promoting stromal cells, CD204 (+) TAMs, and podoplanin (+) CAFs is characteristic of the tumor microenvironment containing CAIX (+) CAFs, which contributes to an increase in aggressive behavior in lung adenocarcinoma with hypoxic regions.

RhoA regulates lipopolysaccharide‑induced lung cell injury via the Wnt/β‑catenin pathway

Ras homolog family member A (RhoA) has been reported to be involved in numerous biological processes; however, the effects of RhoA on acute lung injury (ALI) have yet to be reported. The present study aimed to explore how RhoA affects cell viability, reactive oxygen species (ROS) activity and cell apoptosis in a cell model of lipopolysaccharide (LPS)‑induced ALI. An MTT assay, flow cytometry, reverse transcription‑quantitative polymerase chain reaction and western blotting were used to determine the effects of RhoA on cell viability, apoptosis and ROS activity. The results demonstrated that RhoA inactivation was able to promote cell viability, and decrease apoptosis and ROS activity of LPS‑treated cells. The results of western blotting indicated that RhoA activated the downstream Wnt/β‑catenin signaling pathway and inhibited the expression of apoptotic factors. These findings suggested that RhoA may be involved in ALI progression and could be a novel therapeutic target for this disease.

Podoplanin increases the migration of human fibroblasts and affects the endothelial cell network formation: A possible role for cancer-associated fibroblasts in breast cancer progression

In our previous studies we showed that in breast cancer podoplanin-positive cancer-associated fibroblasts correlated positively with tumor size, grade of malignancy, lymph node metastasis, lymphovascular invasion and poor patients’ outcome. Therefore, the present study was undertaken to assess if podoplanin expressed by fibroblasts can affect malignancy-associated properties of breast cancer cells. Human fibroblastic cell lines (MSU1.1 and Hs 578Bst) overexpressing podoplanin and control fibroblasts were co-cultured with breast cancer MDA-MB-231 and MCF7 cells and the impact of podoplanin expressed by fibroblasts on migration and invasiveness of breast cancer cells were studied in vitro. Migratory and invasive properties of breast cancer cells were not affected by the presence of podoplanin on the surface of fibroblasts. However, ectopic expression of podoplanin highly increases the migration of MSU1.1 and Hs 578Bst fibroblasts. The present study also revealed for the first time, that podoplanin expression affects the formation of pseudo tubes by endothelial cells. When human HSkMEC cells were co-cultured with podoplanin-rich fibroblasts the endothelial cell capillary-like network was characterized by significantly lower numbers of nodes and meshes than in co-cultures of endothelial cells with podoplanin-negative fibroblasts. The question remains as to how our experimental data can be correlated with previous clinical data showing an association between the presence of podoplanin-positive cancer-associated fibroblasts and progression of breast cancer. Therefore, we propose that expression of podoplanin by fibroblasts facilitates their movement into the tumor stroma, which creates a favorable microenvironment for tumor progression by increasing the number of cancer-associated fibroblasts, which produce numerous factors affecting proliferation, survival and invasion of cancer cells. In accordance with this, the present study revealed for the first time, that such podoplanin-mediated effects can affect tube formation by endothelial cells and participate in their pathological properties in the tumor context. Our experimental data were supported by clinical studies. First, when IDC and DCIS were analyzed by immunohistochemistry according to the presence of podoplanin-expressing cells, the numbers of cancer-associated fibroblasts with high expression of this glycoprotein were significantly higher in IDC than in DCIS cases. Second, using immunofluorescence, the co-localization of PDPN-positive CAFs with blood vessels stained with antibody directed against CD34 was observed in tumor stroma of IDC samples.

Bone marrow mesenchymal stromal cell (MSC) gene profiling in chronic myeloid leukemia (CML) patients at diagnosis and in deep molecular response induced by tyrosine kinase inhibitors (TKIs)

Although it has been well-demonstrated that bone marrow mesenchymal stromal cells (MSCs) from CML patients do not belong to the Ph1-positive clone, there is growing evidence that they could play a role in the leukemogenesis process or the protection of leukemic stem cells from the effects of tyrosine kinase inhibitors (TKIs). The aim of the present study was to identify genes differentially expressed in MSCs isolated from CML patients at diagnosis (CML-MSCs) as compared to MSCs from healthy controls. Using a custom gene-profiling assay, we identified six genes over-expressed in CML-MSCs (BMP1, FOXO3, MET, MITF, NANOG, PDPN), with the two highest levels being documented for PDPN (PODOPLANIN) and NANOG. To determine whether this aberrant signature persisted in patients in deep molecular response induced by TKIs, we analyzed MSCs derived from such patients (MR-MSCs). This analysis showed that, despite the deep molecular responses, BMP1, MET, MITF, NANOG, and PDPN mRNA were upregulated in MR-MSCs. Moreover, BMP1, MITF, and NANOG mRNA expressions in MR-MSCs were found to be intermediate between control MSCs and CML-MSCs. These results suggest that CML-MSCs exhibit an abnormal gene expression pattern which might have been established during the leukemogenic process and persist in patients in deep molecular response.

Pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis in tumor lymphangiogenesis and lymphatic metastasis

Precondition for tumor lymphatic metastasis is that tumor cells induce formation of original and newborn lymphatic vessels and invade surrounding lymphatic vessels in tumor stroma, while some pathway-related molecules play an important role in mechanisms associated with proliferation and migration of lymphatic endothelial cells (LECs) and tumor cells. In lymphangiogenesis and lymphatic metastasis, the pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis, such as Furin-like enzyme, CNTN1, Prox1, LYVE-1, Podoplanin, SOX18, SDF1 and CXCR4, are direct constitutors as a portion of VEGFC/D-VEGFR3/NRP2 axis, and their biological activities rely on this ligand-receptor system. These axis-related signal molecules could gradually produce waterfall-like cascading effects, mediate differentiation and maturation of LECs, remodel original and neonatal lymphatic vessels, as well as ultimately promote tumor cell chemotaxis, migration, invasion and metastasis to lymphoid tracts. This review summarizes the structure and function features of pathway-related molecules of VEGFC/D-VEGFR3/NRP2 axis, the expression changes of these molecules in different anatomic organs or histopathologic types or development stages of various tumors, the characteristics of transduction, implementation, integration of signal networks, the interactive effects on biological behaviors between tumor cells and lymphatic endothelial cells, and their molecular mechanisms and significances in tumor lymphangiogenesis and lymphatic metastasis.

Podoplanin-expressing cancer-associated fibroblasts inhibit small cell lung cancer growth

Cancer-associated fibroblasts (CAFs) expressing podoplanin (PDPN) are a favorable prognosticator in surgically resected small cell lung cancer (SCLC). Here we explore whether CAFs expressing PDPN influence proliferation of SCLC cells. Compared with control group (SCLC cells co-cultured with CAFs-Ctrl), numbers of SCLC cells co-cultured with CAFs overexpressing PDPN were decreased. Suppression of PDPN expression by shRNA in CAFs resulted in increased numbers of SCLC cells. In surgically resected human SCLC specimens, the frequency of Geminin-positive cancer cells was significantly higher in the cases with PDPN-positive CAFs than in the cases with PDPN-negative CAFs. Thus CAFs expressing PDPN inhibit growth of SCLC cells, suggesting that CAFs expressing PDPN represent a tumor inhibitory stromal cell component in SCLC.

Aggressive tumor microenvironment of solid predominant lung adenocarcinoma subtype harboring with epidermal growth factor receptor mutations

INTRODUCTION

Tumor microenvironment critically affects cancer progression. This study aimed to identify differences in microenvironments of lung adenocarcinomas with epidermal growth factor receptor (EGFR) mutations by histological subtypes.

METHODS

The study cohort included 214 lung adenocarcinomas harboring EGFR mutations. We analyzed clinicopathological characteristics of lepidic (LPA), papillary (PPA), acinar (APA), and solid-predominant adenocarcinoma (SPA) subtypes, and examined expression levels of EGFR, E-cadherin, ezrin, laminin-5, ALDH1, and PD-L1 in cancer cells, and of CD34, CD204, podoplanin (PDPN), and FoxP3 in stromal cells in 4 subtypes (n=20 each).

RESULTS

SPA displayed significantly more frequent lymph node metastasis, lymphovascular invasion, and worse prognosis than the other subtypes. Ezrin expression levels in SPA were also significantly higher than in LPA, PPA, or APA (P<0.05, all). Laminin-5 and PD-L1 expression levels in SPA were significantly higher than in LPA (P<0.01 for both) and PPA (P<0.01 for both) and tended to be higher than in APA (laminin-5: P=0.096, PD-L1: P=0.081). Furthermore, SPA displayed higher levels of PDPN (+) cancer-associated fibroblasts (P<0.01) and CD204 (+) tumor-associated macrophages (P<0.05) than the other subtypes.

CONCLUSION

Compared with other predominant subtypes with EGFR mutations, the microenvironment of SPA with EGFR mutations is characterized by cancer cells with higher invasive and immune evasion potential and more abundant stromal cells with tumor-promoting functions, which would contribute to the more aggressive behavior of SPA.

PKA and CDK5 can phosphorylate specific serines on the intracellular domain of podoplanin (PDPN) to inhibit cell motility

Podoplanin (PDPN) is a transmembrane glycoprotein that promotes tumor cell migration, invasion, and cancer metastasis. In fact, PDPN expression is induced in many types of cancer. Thus, PDPN has emerged as a functionally relevant cancer biomarker and chemotherapeutic target. PDPN contains 2 intracellular serine residues that are conserved between species ranging from mouse to humans. Recent studies indicate that protein kinase A (PKA) can phosphorylate PDPN in order to inhibit cell migration. However, the number and identification of specific residues phosphorylated by PKA have not been defined. In addition, roles of other kinases that may phosphorylate PDPN to control cell migration have not been investigated. We report here that cyclin dependent kinase 5 (CDK5) can phosphorylate PDPN in addition to PKA. Moreover, results from this study indicate that PKA and CDK5 cooperate to phosphorylate PDPN on both intracellular serine residues to decrease cell motility. These results provide new insight into PDPN phosphorylation dynamics and the role of PDPN in cell motility. Understanding novel mechanisms of PDPN intracellular signaling could assist with designing novel targeted chemotherapeutic agents and procedures.

Podoplanin-expressing cancer-associated fibroblasts lead and enhance the local invasion of cancer cells in lung adenocarcinoma

Cancer-associated fibroblasts (CAFs) communicate with cancer cells and play important roles in cancer invasion. We previously reported that local invasion of cancer cells was frequently observed in lung adenocarcinoma patients with podoplanin (PDPN)-expressing CAFs. However, the underlying mechanisms of this phenomenon have remained unclear. In this study, we established a novel collagen invasion assay model in which cancer cells and CAFs were cocultured; we analyzed the mechanisms governing how cancer cell invasion was promoted by PDPN(+)CAFs. By observing the dynamic movement of both CAFs and cancer cells in the collagen matrix, we found that PDPN(+)CAFs invaded the matrix to a greater extent, with more cancer cells invading within the "tracks" created by the CAFs, compared with control CAFs. The knockdown of PDPN in CAFs decreased the invasion of both the CAFs and the cancer cells. PDPN(+)CAFs displayed a higher RhoA activity and treatment with a ROCK inhibitor cancelled the increased invasion ability of PDPN(+)CAFs and subsequently decreased the number of invaded cancer cells. After intravenous injection in the mouse tail vein, PDPN(+)CAFs invaded and promoted cancer cell invasion into the lung parenchyma, compared with control CAFs. Among the patients with lung adenocarcinoma, we observed some cases with PDPN(+)CAFs at the invasive front of the tumor. These cases predominantly exhibited pleural invasion of cancer cells, known as pathological invasiveness. Our results indicated that PDPN(+)CAFs were tumor-promoting CAFs that lead and enhance the local invasion of cancer cells, suggesting that the invasion activity of CAFs themselves could be rate-determining for cancer cell invasion.

Podoplanin-positive cancer-associated fibroblasts in the tumor microenvironment induce primary resistance to EGFR-TKIs in lung adenocarcinoma with EGFR mutation

PURPOSE

The biologic characteristics of microenvironmental constituents, especially cancer-associated fibroblasts (CAF), can be key regulators of the cellular sensitivity to molecular-targeted therapy. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) have marked therapeutic effects against non-small cell lung cancer (NSCLC) with EGFR mutations, but some patients have exhibited primary resistance to EGFR-TKIs. We recently reported that podoplanin-positive fibroblasts are associated with a tumor-promoting phenotype of CAFs in lung adenocarcinoma. The aim of this study was to evaluate whether the susceptibility of NSCLC to EGFR-TKIs could be affected by podoplanin-expressing CAFs.

EXPERIMENTAL DESIGN

We evaluated the EGFR-TKI sensitivity of EGFR-mutant lung adenocarcinoma cell lines cocultured with podoplanin-expressing CAFs. We also examined the association between the expression of podoplanin in CAFs in surgical specimens and EGFR-TKI response of postoperative recurrent patients with EGFR mutations (N = 106).

RESULTS

Lung adenocarcinoma cell lines became more resistant to EGFR-TKI when cocultured with podoplanin-expressing CAFs, compared with control CAFs in vitro. The knockdown of podoplanin expression on CAFs cancelled the resistance to EGFR-TKIs in cancer cells. Compared with control CAFs, the cancer cells that were cocultured with podoplanin-positive CAFs continued to exhibit significantly higher p-ERK levels after treatment with gefitinib. Furthermore, postoperative recurrent patients with podoplanin-positive CAFs had a significantly lower overall response rate to EGFR-TKIs compared with those with podoplanin-negative CAFs (53% vs. 83%; P < 0.01).

CONCLUSIONS

Podoplanin-positive CAFs play an important role in primary resistance to EGFR-TKIs and may be an ideal therapeutic target for use in combination therapy with EGFR-TKIs.

Podoplanin expressing cancer-associated fibroblasts in oral cancer

Podoplanin is a mucin-type glycoprotein widely used as a lymphatic endothelial marker. It is well known that podoplanin is expressed in various neoplasms including oral squamous cell carcinoma (OSCC). Apart from podoplanin expression in cancer cells, recent studies have suggested that podoplanin expression in stromal cancer-associated fibroblasts (CAFs) may be an indicator of poor prognosis in various cancers. In the present study, we performed immunohistochemical analyses of podoplanin and alpha-smooth muscle actin (α-SMA) in OSCC in order to clarify the significance of podoplanin-positive CAFs. Paraffin-embedded tissue specimens of 69 primary and 29 corresponding metastatic lesions in lymph nodes were examined immunohistochemically using antibodies against podoplanin and α-SMA. Podoplanin-positive stromal fibroblasts were detected in 51 (73.9%) of the 69 primary OSCCs and 24 (82.8%) of the 29 lymph nodes metastases. α-SMA immunoreactivity was observed in 39 (56.5%) of the primaries and 24 (82.8%) of the metastases. Further examination showed that 38 (74.5%) of the primary lesions and 23 (95.8%) of the metastases with podoplanin positivity were also positive for α-SMA. In addition, the intensity of α-SMA immunoreactivity increased as that of podoplanin became stronger. Podoplanin-positive CAFs are considered to be myofibroblasts that may contribute to progression of oral cancer.

Significance of podoplanin expression in cancer-associated fibroblasts: a comprehensive review

Cancer-associated fibroblasts (CAFs) are well-known to be part of the tumor microenvironment. This heterogeneous population of cells of the tumor microenvironment via secretion of various growth factors and cytokines was shown to contribute to increased cancer cell proliferation rate, migration, invasiveness and other key processes such as angiogenesis and lymphangiogenesis. Recent studies identified podoplanin as a marker of CAFs in various malignancies and its expression in these cells was shown to influence cancer progression. In some studies it yielded a prognostic impact on patient survival which was strongly dependent on the entity of the tumor. This review summarizes recent findings concerning the biology of podoplanin in cancer progression with particular emphasis on its expression in CAFs.

Serines in the intracellular tail of podoplanin (PDPN) regulate cell motility

Podoplanin (PDPN) is a transmembrane receptor that affects the activities of Rho, ezrin, and other proteins to promote tumor cell motility, invasion, and metastasis. PDPN is found in many types of cancer and may serve as a tumor biomarker and chemotherapeutic target. The intracellular region of PDPN contains only two serines, and these are conserved in mammals including mice and humans. We generated cells from the embryos of homozygous null Pdpn knock-out mice to investigate the relevance of these serines to cell growth and migration on a clear (PDPN-free) background. We report here that one or both of these serines can be phosphorylated by PKA (protein kinase A). We also report that conversion of these serines to nonphosphorylatable alanine residues enhances cell migration, whereas their conversion to phosphomimetic aspartate residues decreases cell migration. These results indicate that PKA can phosphorylate PDPN to decrease cell migration. In addition, we report that PDPN expression in fibroblasts causes them to facilitate the motility and viability of neighboring melanoma cells in coculture. These findings shed new light on how PDPN promotes cell motility, its role in tumorigenesis, and its utility as a functionally relevant biomarker and chemotherapeutic target.

Podoplanin expressing cancer associated fibroblasts are associated with unfavourable prognosis in adenocarcinoma of the esophagus

Overexpression of the mucin-type sialoglycoprotein podoplanin in cancer associated fibroblasts (CAFs) was recently shown to be associated with tumor progression, metastasis and poor prognosis in lung and breast cancer. Here we investigate the role of podoplanin expressing CAFs in esophagal adenocarcinoma (AC), its precursor lesions and metastases. Podoplanin expression was investigated immunohistochemically in 200 formalin-fixed, paraffin embedded specimens of invasive esophagal ACs, their corresponding metastases and 35 precursor lesions. Podoplanin expressing CAFs (CAF+) were observed in 22 % of patients with invasive AC, but not in precursor lesions. CAF+ correlated with tumor stage (p = 0.004), lymphovascular tumor invasion (p = 0.018) and lymph node metastasis (p = 0.0016). Patients with CAF+ had a significant shorter disease free and overall survival (p < 0.05, Cox regression). Podoplanin expressing CAFs were only rarely observed in lymph node and distant metastases, as well as in local recurrences of ACs. Podoplanin expression in AC tumor cells was seen in only four cases. In around 20 % of patients with esophagal AC, podoplanin expressing CAFs are evident, defining a high risk subgroup. In these patients, podoplanin expressing CAFs might represent new therapeutical targets.

Podoplanin: emerging functions in development, the immune system, and cancer

Podoplanin (PDPN) is a well-conserved, mucin-type transmembrane protein expressed in multiple tissues during ontogeny and in adult animals, including the brain, heart, kidney, lungs, osteoblasts, and lymphoid organs. Studies of PDPN-deficient mice have demonstrated that this molecule plays a critical role in development of the heart, lungs, and lymphatic system. PDPN is widely used as a marker for lymphatic endothelial cells and fibroblastic reticular cells of lymphoid organs and for lymphatics in the skin and tumor microenvironment. Much of the mechanistic insight into PDPN biology has been gleaned from studies of tumor cells; tumor cells often upregulate PDPN as they undergo epithelial-mesenchymal transition and this upregulation is correlated with increased motility and metastasis. The physiological role of PDPN that has been most studied is its ability to aggregate and activate CLEC-2-expressing platelets, as PDPN is the only known endogenous ligand for CLEC-2. However, more recent studies have revealed that PDPN also plays crucial roles in the biology of immune cells, including T cells and dendritic cells. This review will provide a comprehensive overview of the diverse roles of PDPN in development, immunology, and cancer.