Dasatinib reverses cancer-associated fibroblasts (CAFs) from primary lung carcinomas to a phenotype comparable to that of normal fibroblasts.

Cancer associated fibroblasts (CAFs) play a critical role for growth, invasion, and metastasis of cancer. Therefore, targeting CAFs with small molecule inhibitors may be an attractive anti-tumor strategy. The current study aims to identify small molecule kinase inhibitors affecting CAF's growth and to characterize the biological effects of active compounds on primary CAFs from lung cancer. We screened two individual CAF strains for their sensitivity to a panel of 160 kinase inhibitors. Five kinase inhibitors were identified inhibiting more than 50% of the growth of both cell lines. Three of them were inhibitors of PDGFR at nanomolar concentrations. Therefore, we further tested the FDA approved PDGFR inhibitors Dasatinib, Nilotinib, Sorafenib, and Imatinib. All 37 CAF strains investigated were highly sensitive to Dasatinib at clinically relevant concentrations. Imatinib was slightly less effective, whereas the inhibitory effects of Nilotinib and Sorafenib were significantly less pronounced.We investigated the effect of Dasatinib on the CAF transcriptome by microarray analysis of 9 individual CAF strains. 492 genes were identified whose expression was changed at least twofold. 104 of these encoded cell cycle related proteins with 97 of them being downregulated by Dasatinib. The majority of regulated genes, however, were of diverse biological functions not directly related to proliferation. We compared this Dasatinib expression signature to previously described differential signatures of normal tissue associated fibroblasts (NAFs) and CAFs and to a signature of fibroblast serum response. There was a significant overlap between genes regulated by Dasatinib and serum repression genes. More importantly, of the 313 genes downregulated by Dasatinib 64 were also reduced in NAFs compared to CAFs. Furthermore, 26 of 179 genes identified as upregulated by Dasatinib were also found to be elevated in NAFs compared to CAFs. These data demonstrate that Dasatinib partially reverses the phenotype of CAFs to a normal fibroblast like phenotype. This is further supported by the finding that incubation of tumor cells with conditioned medium from CAFs pre-incubated with Dasatinib significantly reduced tumor cell proliferation, suggesting that Dasatinib partially reverses the CAF mediated tumor promoting effect. Therefore, targeting CAFs with Dasatinib represents a promising therapeutic principle.

Cancer cells cue the p53 response of cancer-associated fibroblasts to cisplatin.

Current understanding of the p53 response is based mainly upon in vitro studies of homogeneous cell populations. However, there is little information on whether the same principles operate within heterogeneous tumor tissues that are comprised of cancer cells and other cell types, including cancer-associated fibroblasts (CAF). Using ex-vivo tissue cultures, we investigated p53 status and responses to cisplatin in tumor cells and CAFs from tissue specimens isolated from 32 lung cancer patients. By comparing cultivated tissue slices with the corresponding tumor tissues fixed immediately after surgery, we found that morphology, proliferation, and p53 staining pattern were preserved during cultivation. Unexpectedly, when CAFs were analyzed, p53 accumulation and induction of p21 was observed only in tumors with constitutively low p53 protein and accumulation upon cisplatin treatment. In contrast, in tumors with no p53 accumulation in cancer cells there was also no p53 accumulation or p21 induction in adjacent CAFs. Furthermore, induction of cisplatin-induced apoptosis in CAFs was selectively observed in tumors characterized by a parallel induction of cancer cell death. Our findings reveal an interdependence of the p53 response in cancer cells and adjacent CAFs within tumor tissues, arguing that cancer cells control the response of their microenvironment to DNA damage.

Transcriptional control of a plant stem cell niche.

Despite the independent evolution of multicellularity in plants and animals, the basic organization of their stem cell niches is remarkably similar. Here, we report the genome-wide regulatory potential of WUSCHEL, the key transcription factor for stem cell maintenance in the shoot apical meristem of the reference plant Arabidopsis thaliana. WUSCHEL acts by directly binding to at least two distinct DNA motifs in more than 100 target promoters and preferentially affects the expression of genes with roles in hormone signaling, metabolism, and development. Striking examples are the direct transcriptional repression of CLAVATA1, which is part of a negative feedback regulation of WUSCHEL, and the immediate regulation of transcriptional repressors of the TOPLESS family, which are involved in auxin signaling. Our results shed light on the complex transcriptional programs required for the maintenance of a dynamic and essential stem cell niche.

Dual roles of the bZIP transcription factor PERIANTHIA in the control of floral architecture and homeotic gene expression.

Flowers develop from floral meristems, which harbor stem cells that support the growth of floral organs. The MADS domain transcription factor AGAMOUS (AG) plays a central role in floral patterning and is required not only for the specification of the two reproductive organ types, but also for termination of stem cell fate. Using a highly conserved cis-regulatory motif as bait, we identified the bZIP transcription factor PERIANTHIA (PAN) as a direct regulator of AG in Arabidopsis. PAN and AG expression domains overlap, and mutations in either the PAN-binding site or PAN itself abolish the activity of a reporter devoid of redundant elements. Whereas under long-day conditions pan mutants have merely altered floral organ number, they display in addition typical AG loss-of-function phenotypes when grown under short days. Consistently, we found reduced AG RNA levels in these flowers. Finally, we show that PAN expression persists in ag mutant flowers, suggesting that PAN and AG are engaged in a negative-feedback loop, which might be mediated by the stem-cell-inducing transcription factor WUSCHEL (WUS).