Hiroko Hashimoto

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. Clin Cancer Res; 21(3); 642–51. ©2014 AACR.

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

There is growing evidence that stromal fibroblasts can promote tumor progression via several mechanisms. We previously reported that podoplanin (PDPN) expressed on stromal fibroblasts is functionally protein responsible for the promotion of tumor formation in mouse subcutaneous tissue. The purpose of the present study was to reveal the molecular mechanism by which PDPN on stromal fibroblasts promotes tumor formation. The subcutaneous co-injection of the human lung adenocarcinoma cell line A549 and human fibroblasts (hFbs) overexpressing wild-type podoplanin (WT-PDPN) promoted subcutaneous tumor formation, compared with the co-injection of A549 and control hFbs (64% vs 21%). On the other hand, hFbs expressing PDPN mutant in which the cytoplasmic domain of PDPN was deleted (PDPN-Del.IC), resulted in a relatively lower level of tumor formation (33%). Since PDPN reportedly regulates RhoA activity through its cytoplasmic domain, we measured the activation state of RhoA in hFbs expressing WT-PDPN. RhoA activity was 2.7-fold higher in WT-PDPN expressing hFbs than in control hFbs. Furthermore, the subcutaneous co-injection of hFbs expressing constitutive active RhoA (G14VRhoA) and A549 cells enhanced tumor formation compared with the co-injection of the same cell line and control hFbs. These results indicate that enhanced RhoA activity in hFbs expressing PDPN may be one of the mechanisms resulting in the promotion of tumor formation, suggesting that biomechanical remodeling of the microenvironment by stromal fibroblasts may play important roles in tumor progression.

CD200-positive cancer associated fibroblasts augment the sensitivity of Epidermal Growth Factor Receptor mutation-positive lung adenocarcinomas to EGFR Tyrosine kinase inhibitors

Cancer associated fibroblasts (CAFs) play important roles in the chemotherapeutic process, especially through influencing the resistance of tumor cells to molecular targeted therapy. Here we report the existence of a special subpopulation of patient-specific-CAFs that augment the sensitivity of EGFR gene mutation-positive lung cancer to the EGFR-tyrosine kinase inhibitor (EGFR-TKI), gefitinib. When cocultured with EGFR mutation positive lung cancer cells, these CAFs increased the apoptic effect of gefitinib on cancer cells, whereas, in the absence of gefitinib, they did not affect cancer cell viability. The assay using different single cell-derived clones demonstrated that the aforementioned sensitizing ability is clone-specific. Microarray analysis revealed that CD200 was expressed at much higher levels in this CAFs. Knocking down of CD200 expression deprived CAFs of their sensitizing potential, suggesting that CD200 is the functional molecule responsible for the effect. Immunohistochemical analysis of samples from patients receiving postoperative gefitinib treatment revealed that the individuals whose resected lung adenocarcinomas contained CD200-positive CAFs tended to have longer progression free survival of gefitinib when they recurred after surgery. These results suggest that CD200-positive CAFs can augment the sensitivity to EGFR-TKIs and may possess far reaching applications in the therapeutic use of EGFR-TKIs.

Morphophenotype of floating colonies derived from a single cancer cell has a critical impact on tumor-forming activity.

The anchorage‐independent colony growth of cancer cells is reportedly correlated with the tumor‐forming activity; however, the correlation between the morphophenotype of each colony and the tumor‐forming activity has not been clarified. To assess this problem, we cultured single A549 cells (human lung adenocarcinoma cell line) in growth medium in individual wells (n = 426) for 14 days under anchorage‐independent conditions and analyzed the resulting growth characteristics. The single A549 cells formed various sizes of floating colonies. The proportion of large colonies (>400 μm) was 3.8% and this proportion increased dramatically with the exogenous addition of EGF (21.6%) or HGF (27.6%). Morphologically, the floating colonies could be divided into: (ii) Type A, spheroid colony; and (ii) Type B, dispersed villous colony. The Type B colonies expressed significantly higher levels of epithelial‐mesenchymal transition (EMT)‐related mRNAs (Snail 1, ZEB 1, and ZEB2) than the Type A colonies. Furthermore, the subcutaneous injection of a single cell‐derived colony with a large size and a Type B morphology resulted in more efficient tumor formation. The present results indicated that the morphophenotypes of floating colonies derived from single cancer cells have a critical impact on tumor‐forming activity.

Collagen type I induces EGFR-TKI resistance in EGFR-mutated cancer cells by mTOR activation through Akt-independent pathway

Primary resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR‐TKIs) is a serious problem in lung adenocarcinoma patients harboring EGFR mutations. The aim of this study was to examine whether and how collagen type I (Col I), the most abundantly deposited matrix in tumor stroma, affects EGFR‐TKI sensitivity in EGFR‐mutant cells. We evaluated the EGFR‐TKI sensitivity of EGFR‐mutated cancer cells cultured with Col I. Changes in the activation of downstream signaling molecules of EGFR were analyzed. We also examined the association between the Col I expression in tumor stroma in surgical specimens and EGFR‐TKI response of postoperative recurrence patients with EGFR mutations. Compared to cancer cells without Col I, the survival rate of cancer cells cultured with Col I was significantly higher after EGFR‐TKI treatment. In cancer cells cultured with and without Col I, EGFR‐TKI suppressed the levels of phosphorylated (p‐)EGFR, p‐ERK1/2, and p‐Akt. When compared to cancer cells without Col I, expression of p‐P70S6K, a hallmark of mTOR activation, was dramatically upregulated in cancer cells with Col I. This activation was maintained even after EGFR‐TKI treatment. Simultaneous treatment with EGFR‐TKI and mTOR inhibitor abrogated Col I‐induced resistance to EGFR‐TKI. Patients with Col I‐rich stroma had a significantly shorter progression‐free survival time after EGFR‐TKI therapy (238 days vs 404 days; P < .05). Collagen type I induces mTOR activation through an Akt‐independent pathway, which results in EGFR‐TKI resistance. Combination therapy using EGFR‐TKI and mTOR inhibitor could be a possible strategy to combat this resistance.

Clonal heterogeneity in osteogenic potential of lung cancer-associated fibroblasts: promotional effect of osteogenic progenitor cells on cancer cell migration

BackgroundCancer-associated fibroblasts (CAFs) consist of heterogeneous cell population in terms of their differentiation potential. The functional differences in tumor progression between CAFs with mesenchymal stem/progenitor cells (MSCs/MPCs) characteristics and CAFs without MSCs/MPCs characteristics are not clarified.MethodsCAFs and vascular adventitial fibroblasts (VAFs, which contain MSCs/MPCs) were isolated from nine primary lung cancers and were cultured in osteogenic or adipogenic medium to assess their multi-lineage differentiation. Next, we established nine single-cell-derived clones from the primary culture of CAFs and examined their differentiation potential. The effects of each single-cell-derived clone on the proliferation and migration of lung adenocarcinoma cell line, A549, were analyzed.ResultsThe nine samples of VAFs and CAFs showed various degrees of osteogenic differentiation. Although the VAFs displayed the ability to undergo adipogenic differentiation, all cases of the CAFs did not. CAFs clones presented varying degrees of osteogenic differentiation. Four clones displayed comparable levels of osteogenic potential with that of the VAFs, and two clones were completely negative. As compared to the CAFs clones that possessed lower osteogenic potential, CAFs clones with higher osteogenic potential did not confer proliferative activity in A549 cells. On the contrary, these clones significantly promoted the migration of A549 cells as compared to the clones with lower osteogenic potential.ConclusionOur studies clearly indicate that CAFs derived from lung cancer are heterogeneous population that consists of cells with varying osteogenic potentials and that CAFs with higher osteogenic potential have a greater tumor-promoting function through the enhancement of cancer cell migration.

A novel method to generate single-cell-derived cancer-associated fibroblast clones

BackgroundCancer-associated fibroblasts (CAFs) communicate with cancer cells to play important roles in tumor progression. However, CAFs have heterogeneous phenotypes and functions. To understand how much of this heterogeneity relates to different biological responses, a more efficient method of generating single-cell-derived CAF clones is required.MethodWe transduced two primary CAF cultures (CAFs-608 and CAFs-621) from lung adenocarcinoma with human telomerase reverse transcriptase (hTERT), mutant forms of cyclin dependent kinase 4 (CDK4R24C) independently and in combination (hTERT/CDK4R24C). After live imaging of each sorted-single cell, we evaluated the numbers of successfully established clones from CAFs-hTERT, CAFs-CDK4R24C, and CAFs-hTERT/CDK4R24C. Furthermore, we examined the expression levels of genes associated with tumor promoting pathways in established clones by qRT-PCR.ResultsOverexpression of hTERT and CDK4R24C efficiently extended the lifespan of both CAFs-608 and CAFs-621. The number of established CAF clones was highest for CAFs-hTERT/CDK4R24C, with 57 and 62 clones established from CAFs-608 and CAFs-621, respectively. Conversely, 16 and 11 CAFs-hTERT clones were derived from CAFs-608 and CAFs-621, respectively and 10 and 8 CAFs-CDK4R24C clones were from CAFs-608 and CAFs-621, respectively. TGF-b, ATCA2, and HSF1 mRNA levels differed in individual clones established from CAFs-hTERT/CDK4R24C. The expression levels of ATCA2 and HSF1 were much higher in one clone than in the other established clones and the parental CAFs.ConclusionOur results show that combined exogenous expression of hTERT and mutant CDK4 is an effective method to generate single-cell-derived CAF clones. This provides an innovative and suitable approach to investigate the heterogeneous function and phenotype of CAFs.