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Dbs was identified initially as a transforming protein and is a member of the Dbl family of proteins (>20 mammalian members). Here we show that Dbs, like its rat homolog Ost and the closely related Dbl, exhibited guanine nucleotide exchange activity for the Rho family members RhoA and Cdc42, but not Rac1, in vitro. Dbs transforming activity was blocked by specific inhibitors of RhoA and Cdc42 function, demonstrating the importance of these small GTPases in Dbs-mediated growth deregulation. Although Dbs transformation was dependent upon the structural integrity of its pleckstrin homology (PH) domain, replacement of the PH domain with a membrane localization signal restored transforming activity. Thus, the PH domain of Dbs (but not Dbl) may be important in modulating association with the plasma membrane, where its GTPase substrates reside. Both Dbs and Dbl activate multiple signaling pathways that include activation of the Elk-1, Jun, and NF-kappaB transcription factors and stimulation of transcription from the cyclin D1 promoter. We found that Elk-1 and NF-kappaB, but not Jun, activation was necessary for Dbl and Dbs transformation. Finally, we have observed that Dbl and Dbs regulated transcription from the cyclin D1 promoter in a NF-kappaB-dependent manner. Previous studies have dissociated actin cytoskeletal activity from the transforming potential of RhoA and Cdc42. These observations, when taken together with those of the present study, suggest that altered gene expression, and not actin reorganization, is the critical mediator of Dbl and Rho family protein transformation.

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Deletion of the NH(2)-terminal 65 amino acids of proto-Vav (to form onco-Vav) activates its transforming activity, suggesting that these sequences serve a negative regulatory role in Vav function. However, the precise role of these NH(2)-terminal sequences and whether additional NH(2)-terminal sequences are also involved in negative regulation have not been determined. Therefore, we generated additional NH(2)-terminal deletion mutants of proto-Vav that lack the NH(2)-terminal 127, 168, or 186 amino acids, and assessed their abilities to cause focus formation in NIH 3T3 cells and to activate different signaling pathways. Since Vav mutants lacking 168 or 186 NH(2)-terminal residues showed a several 100-fold greater focus forming activity than that seen with deletion of 65 residues, residues spanning 66 to 187 also contribute significantly to negative regulation of Vav transforming activity. The increase in Vav transforming activity correlated with the activation of the c-Jun, Elk-1, and NF-kappaB transcription factors, as well as increased transcription from the cyclin D1 promoter. Tyrosine 174 is a key site of phosphorylation by Lck in vitro and Lck-mediated phosphorylation has been shown to be essential for proto-Vav GEF function in vitro. However, we found that an NH(2)-terminal Vav deletion mutant lacking this tyrosine residue (DeltaN-186 Vav) retained the ability to be phosphorylated by Lck in vivo and Lck still caused enhancement of DeltaN-186 Vav signaling and transforming activity. Thus, Lck can stimulate Vav via a mechanism that does not involve Tyr(174) or removal of NH(2)-terminal regulatory activity. Finally, we found that NH(2)-terminal deletion enhanced the degree of Vav association with the membrane-containing particulate fraction and that an isolated NH(2)-terminal fragment (residues 1-186) could impair DeltaN-186 Vav signaling. Taken together, these observations suggest that the NH(2) terminus may serve as a negative regulator of Vav by intramolecular interaction with COOH-terminal sequences to modulate efficient membrane association.

In the U.S., deaths due to pulmonary embolism (PE) account for 9.2% of all pregnancy related deaths or approximately 1.5 deaths per 100,000 live births. Maternal deaths and maternal morbidity due to PE are more common among women who deliver by cesarean section. In the past decade, the clinical community has increasingly adopted venous thromboembolism (VTE) guidelines and thromboprophylaxis recommendations for pregnant women. Although deep vein thrombosis rates have decreased during this time-period, PE rates have remained relatively unchanged in pregnancy hospitalizations and as a cause of maternal mortality. Changes in the health profile of women who become pregnant, particularly due to maternal age and comorbidities, needs more attention to better understand the impact of VTE risk during pregnancy and the postpartum period.

One of the major goals of researchers in the field of apoptosis is to understand the molecular mechanisms of the various components of the apoptotic pathways, with the hope to identify targets for novel cancer therapies. The discovery of a TNF‐related, apoptosis‐inducing ligand, TRAIL, that kills transformed cells with great specificity in vitro, has provided the hope that TRAIL may be used to induce cell death in tumor cells without affecting normal tissues. However, TRAIL signaling is very complex and a clear understanding of its function is necessary before it can be used in cancer therapy. Complexity of TRAIL‐induced signaling is apparent from its ubiquitous expression, its ability to interact with five receptors, and its tumor‐selective induction of apoptosis. The signaling events that mediate the tumor selectivity of TRAIL‐induced apoptosis and the biological functions of each of the TRAIL receptors are not well characterized. This review will focus on the complexity of TRAIL and the role of c‐FLIP in mediating TRAIL function.

Activated forms of different Rho family members (CDC42, Rac1, RhoA, RhoB, and RhoG) have been shown to transform NIH 3T3 cells as well as contribute to Ras transformation. Rho family guanine nucleotide exchange factors (GEFs) (also known as Dbl family proteins) that activate CDC42, Rac1, and RhoA also demonstrate oncogenic potential. The faciogenital dysplasia gene product, FGD1, is a Dbl family member that has recently been shown to function as a CDC42-specific GEF. Mutations within the FGD1 locus cosegregate with faciogenital dysplasia, a multisystemic disorder resulting in extensive growth impairments throughout the skeletal and urogenital systems. Here we demonstrate that FGD1 expression is sufficient to cause tumorigenic transformation of NIH 3T3 fibroblasts. Although both FGD1 and constitutively activated CDC42 cooperated with Raf and showed synergistic focus-forming activity, both quantitative and qualitative differences in their functions were seen. FGD1 and CDC42 also activated common nuclear signaling pathways. However, whereas both showed comparable activation of c-Jun, CDC42 showed stronger activation of serum response factor and FGD1 was consistently a better activator of Elk-1. Although coexpression of FGD1 with specific inhibitors of CDC42 function demonstrated the dependence of FGD1 signaling activity on CDC42 function, FGD1 signaling activities were not always consistent with the direct or exclusive stimulation of CDC42 function. In summary, FGD1 and CDC42 signaling and transformation are distinct, thus suggesting that FGD1 may be mediating some of its biological activities through non-CDC42 targets.The Rho subfamily of Ras-related GTPases (14 mammalian members) controls multiple aspects of cell behavior, including cytoskeletal rearrangement, nuclear signaling, and cell growth (reviewed in reference 67). For example, CDC42 mediates the induction of actin microspikes and filopodia by bradykinin (26, 33), whereas Rac1 is required for growth factor-induced membrane ruffling and lamellipodia formation (47). In contrast, RhoA regulates the formation of actin stress fibers (46). In Swiss 3T3 cells, the assembly of these structures involves a cascade in which CDC42 activates Rac1, which in turn activates RhoA (33). Rho family proteins also have demonstrated roles in the regulation of gene expression as measured by (i) the transcriptional activation of the serum response factor (SRF) (19), (ii) activation of c-Jun NH 2 -terminal kinase (JNK) and its downstream target c-Jun (10, 32, 35), (iii) activation of the ternary complex factor protein Elk-1 (62), (iv) activation of p38/Mpk2 (63), and (v) regulation of expression from the cyclin D1 promoter (55). Finally, there is growing evidence that the deregulated expression of Rho family members has profound effects on the proliferative potential of cells. Activated derivatives of RhoA, RhoB, Rac1, and CDC42 cause oncogenic transformation when expressed in rodent fibroblast cell lines and may contribute to Ras-mediated malignant transformation (23,39,41,42,53,...

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