No abstract

Exposure of vascular smooth muscle cells to arginine vasopressin (AVP) increases smooth muscle ␣-actin (SM-␣-actin) expression through activation of the SM-␣-actin promoter. The goal of this study was to determine the role of the mitogen-activated protein kinase (MAP kinase) family in regulation of SM-␣-actin expression. AVP activated all three MAP kinase family members: ERKs, JNKs, and p38 MAP kinase. Inhibition of JNKs or p38 decreased AVP-stimulated SM-␣-actin promoter activity, whereas inhibition of ERKs had no effect. A 150-base pair region of the promoter containing two CArG boxes was sufficient to mediate regulation by vasoconstrictors. Mutations in either CArG box decreased AVPstimulated promoter activity. Electrophoretic mobility shift assays using oligonucleotides corresponding to either CArG box resulted in a complex of similar mobility whose intensity was increased by AVP. Antibodies against serum response factor (SRF) completely supershifted this complex, indicating that SRF binds to both CArG boxes. Overexpression of SRF increased basal promoter activity, but activity was still stimulated by AVP. AVP stimulation rapidly increased SRF phosphorylation. These data indicate that both JNKs and p38 participate in regulation of SM-␣-actin expression. SRF, which binds to two critical CArG boxes in the promoter, represents a potential target of these kinases.

No abstract

Cancer progression and metastasis involves interactions between tumor cells and the tumor microenvironment (TME). We reported that mice deficient for cytosolic phospholipase A 2 (cPLA 2 -KO) are protected against the development of lung tumors. The goal of this study was to examine the role of cPLA 2 in the TME. Mouse lung cancer cells (CMT167 and Lewis lung carcinoma cells) injected directly into lungs of syngeneic mice formed a primary tumor, and then metastasized to other lobes of the lung and to the mediastinal lymph nodes. Identical cells injected into cPLA 2 -KO mice showed a dramatic decrease in the numbers of secondary metastatic tumors. This was associated with decreased macrophage staining surrounding the tumor. Wild-type mice transplanted with cPLA 2 -KO bone marrow had a marked survival advantage after inoculation with tumor cells compared with mice receiving wild-type (WT) bone marrow. In vitro, coculturing CMT167 cells with bone marrow-derived macrophages from WT mice increased production of interleukin 6 (IL-6) by cancer cells. This increase was blocked in cocultures using cPLA 2 -KO macrophages. Correspondingly, IL-6 staining was decreased in tumors grown in cPLA 2 -KO mice. These data suggest that stromal cPLA 2 plays a critical role in tumor progression by altering tumor-macrophage interactions and cytokine production.

Pharmacological activators of peroxisome proliferator-activated receptor-␥ (PPAR␥) inhibit growth of non-small-cell lung cancer (NSCLC) cell lines in vitro and in xenograft models. Because these agents engage off-target pathways, we have assessed the effects of PPAR␥ by overexpressing the protein in NSCLC cells. We reported previously that increased PPAR␥ inhibits transformed growth and invasiveness and promotes epithelial differentiation in a panel of NSCLC expressing oncogenic K-Ras. These cells express high levels of cyclooxygenase-2 (COX-2) and produce high levels of prostaglandin E 2 (PGE 2 ). The goal of these studies was to identify the molecular mechanisms whereby PPAR␥ inhibits tumorigenesis. Increased PPAR␥ inhibited expression of COX-2 protein and promoter activity, resulting in decreased PGE 2 production. Suppression of COX-2 was mediated through increased activity of the tumor suppressor phosphatase and tensin homolog, leading to decreased levels of phospho-Akt and inhibition of nuclear factor-B activity. Pharmacological inhibition of PGE 2 production mimicked the effects of PPAR␥ on epithelial differentiation in three-dimensional culture, and exogenous PGE 2 reversed the effects of increased PPAR␥ activity. Transgenic mice overexpressing PPAR␥ under the control of the surfactant protein C promoter had reduced expression of COX-2 in type II cells and were protected against developing lung tumors in a chemical carcinogenesis model. These data indicate that high levels of PGE 2 as a result of elevated COX-2 expression are critical for promoting lung tumorigenesis and that the antitumorigenic effects of PPAR␥ are mediated in part through blocking this pathway.