Abstract. Rat 3Y1 cells acquire metastatic potential when transformed with v-src, and this potential is enhanced by double transformation with v-src and v-los (Taniguchi, S., T. Kawano, T. Mitsudomi, G. Kimura, and T. Baba. 1986. Jpn. J. Cancer Res. 77:1193-1197. We compared the activity of cadherin cell adhesion molecules of normal 3Y1 cells with that of v-src transformed (SR3Y1) and v-src and v-los double transformed (fosSR3Y1) 3Y1 cells. These cells expressed similar amounts of P-cadherin, and showed similar rates of cadherin-mediated aggregation under suspended conditions. However, the aggregates or colonies of these cells were morphologically distinct. Normal 3Y1 cells formed compacted aggregates in which cells are firmly connected with each other, whereas the transformed cells were more loosely associated, and could freely migrate out of the colonies. Overexpression of exogenous E-cadherin in these transformed cells had no significant effect on their adhesive properties. We then found that herbimycin A, a tyrosine kinase inhibitor, induced tighter cell-cell associations in the aggregates of the transformed cells. In contrast, vanadate, a tyrosine phosphatase inhibitor, inhibited the cadherin-mediated aggregation of SR3Y1 and fosSR3Y1 cells but had little effect on that of normal 3Y1 cells. These results suggest that v-src-mediated tyrosine phosphorylation perturbs cadherin function directly or indirectly, and the inhibition of tyrosine phosphorylation restores cadherin action to the normal state. We next studied tyrosine phosphorylation on cadherins and the cadherin-associated proteins, catenins. While similar amounts of catenins were expressed in all of these cells, the 98-kD catenin was strongly tyrosine phosphorylated only in SR3Y1 and fosSR3Y1 cells. Cadherins were also weakly tyrosine phosphorylated only in the transformed cells. The tyrosine phosphorylation of these proteins was enhanced by vanadate, and inhibited by herbimycin A. Thus, the tyrosine phosphorylation of the cadherin-catenin system itself might affect its function, causing instable cell-cell adhesion.

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Targeting the cross-talk between tumor-initiating cells (TICs) and the niche microenvironment is an attractive avenue for cancer therapy. We show here, using a mouse model of squamous cell carcinoma, that TICs play a crucial role in creating a niche microenvironment that is required for tumor progression and drug resistance. Antioxidant activity in TICs, mediated by the transcription factor NRF2, facilitates the release of a nuclear cytokine, interleukin-33 (IL-33). This cytokine promotes differentiation of macrophages that express the high-affinity immunoglobulin E receptor FcεRIα and are in close proximity to TICs. In turn, these IL-33–responding FcεRIα+ macrophages send paracrine transforming growth factor β (TGF-β) signals to TICs, inducing invasive and drug-resistant properties and further upregulating IL-33 expression. This TIC-driven, IL-33–TGF-β feedforward loop could potentially be exploited for cancer treatment.

By using Southern blot analysis, we found that in two cases of human glioblastoma multiforme, cells carried amplified c-erbB genes which bore short deletion mutations within the ligand-binding domain of the epidermal growth factor (EGF) receptor. The products of these mutated c-erbB genes were about 30 kilodalton (kDa) smaller than the normal 170-kDa EGF receptor, and the tumor cell membrane fractions containing the 140-kDa abnormal EGF receptor showed a significant elevation of tyrosine kinase activity without its ligand. In view of the similarity to the activated viral and cellular erbB genes in the avian system, these mutated and overexpressed EGF receptors might play a role in the onset or development of human glioblastoma cells.The c-erbB gene is known to be a proto-oncogene which encodes the epidermal growth factor (EGF) receptor (4,25,30). The v-erbB gene product of avian erythroblastosis virus in chickens has a truncated form of EGF receptor and expresses a higher level of tyrosine kinase activity without its ligand (11). Thus, qualitative and quantitative alterations appear to be crucial for the activation of the c-erbB gene in chickens. In human tumors, amplification of the c-erbB gene has been reported in several squamous cell carcinomas and glioblastomas (3,10,13,14,17,27,29). However, it was not certain whether the c-erbB gene in those tumor cells was also structurally altered.Since the activation of oncogenes in human brain tumors has not yet been extensively studied, we screened several transplantable brain tumors for the presence of abnormal proto-oncogenes, using Southern blot analysis (24). Table 1 lists the tumors tested; six were glioblastomas, and two were ependymomas. The histological characteristics of these tumors have not drastically changed during serial passages in athymic nude mice.Among 19 onc probes employed (myc, N-myc, myb, K-ras, N-ras, sis, src, fpslfes, yes, mos, fos, ros, fms, fgr, abl, rel, rafimil, erbB, erbB-2/neu), no amplification or rearrangement was detected in the transplantable brain tumors except for the v-erbB probe (26); two glioblastomas, GL-3 and GL-5, carried an amplified c-erbB gene (data not shown). Recently Libermann et al. have reported that about one-third of glioblastomas in primary human brain tumors contain an amplified c-erbB gene (13). They also indicated that this gene amplification is associated with a possible DNA rearrangement, but the details were not examined due to the limited availability of primary tumors. The frequency of amplification of the c-erbB gene in transplantable glioblastomas examined here is similar to that of their report.To examine the fine structure of the amplified c-erbB gene in glioblastomas, we used a human EGF receptor cDNA as a probe (kindly provided by I. Pastan, National Cancer Institute, Bethesda, Md.) (16, 28). EcoRI-digested DNAs of GL-3 and GL-5 cells carry a high copy number of the c-erbB gene (Fig. la), and the degree of amplification was almost the same as in the A431 squamous carcinoma cell line, which is known t...

These results indicate that DA inhibits the Na+:HCO3- cotransporter in renal proximal tubules and also suggest that dysregulation of the cotransporter, possibly through the defect in DA1 receptor signaling, could play an important role in development of hypertension in SHRs.