Comparison of polysaccharide glycoconjugates as candidate vaccines to combat Clostridiodes (Clostridium) difficile.

Two known Clostridiodes (Clostridium) difficile surface antigens, a lipoteichoic acid (LTA) and a polysaccharide (PS-II) were isolated and purified in order to prepare glycoconjugate vaccines to the carrier protein human serum albumin utilising a reductive amination strategy. Mice and rabbits were immunized with a prime and two boost strategy and the resulting sera were examined for their ability to recognise the purified homologous antigens and subsequently killed whole cells of C. difficile strains and other Clostridia species. Immunisation derived antisera from rabbits and mice, recognised all strains of C. difficile vegetative cells examined, with generally similar titers from animals that received the LTA or the PS-II conjugates. Sera raised to the LTA conjugates were able to recognise other Clostridia species C. butyricum, C. bifermentans and C. subterminale whereas sera raised to the PS-II conjugates were not. These LTA and PS-II sera recognised live cells in an immunofluorescence assay and were also able to recognise the spore form of the bacterium. This study has confirmed that the LTA and PS-II polysaccharides are both highly conserved surface polymers of C. difficile that are easily accessible to the immune system and as such may have potential as vaccine antigens or as targets for therapeutics to combat C. difficile infection.

Investigating the candidacy of LPS-based glycoconjugates to prevent invasive meningococcal disease: conjugates based on core oligosaccharides.

In this study we have prepared glycoconjugates with core oligosaccharides (OS) from the lipopolysaccharide (LPS) of Neisseria meningitidis, thus avoiding the neo-epitopes of the deacylated lipid A region of the derived LPS molecule identified in our previous studies. A comprehensive investigation was performed with glycoconjugates prepared from the most extended to the most truncated core OS still maintaining the conserved inner core epitope. As previously, we have established reproducible bactericidal killing of the homologous antigen elaborating strain, but a failure to kill wild-type strains. In these studies it was evident that the linker molecules used in the conjugation methodologies were dominating the immune response. However, when galE core OS based conjugates were prepared without utilizing linkers, via direct reductive amination, we failed to generate an immune response to even the homologous antigen. We also identified that immunisation with the galE antigen via linker methodologies provoked an immune response that was dependent upon key residues of the conserved inner core OS structure, whereas the immune responses to lgtB and lgtA antigens did not involve the inner core OS. This comprehensive study has, despite our best efforts, cast significant doubt as to the utility of the conserved inner core region of the meningococcal LPS as a potential vaccine antigen.

Protein prenylation: more than just glue?

As with other lipid modifications of proteins, prenylation now appears to be critically important in the regulation of protein function. Recent research has led to an explosion of information concerning prenylation signals, prenyl transferase enzymes and the role of prenylation in protein-membrane interactions. Experiments have examined the role of prenylation in protein function and the results suggest that protein prenylation may be involved in facilitating proper subcellular localization, promoting protein-protein and protein-membrane interactions and regulating protein function.

Proceedings of a workshop to discuss the epidemiology of invasive Haemophilus influenzae disease with emphasis on serotype a and b in the Americas, 2019.

On March 9, 2019, a one-day workshop titled "The current epidemiology of invasive Haemophilus influenzae disease in the Americas", jointly organized by the Public Health Agency of Canada (PHAC), the Canadian Institute of Health Research (CIHR), and the National Research Council Canada (NRC), brought together experts in the epidemiology and surveillance of invasive Haemophilus influenzae (Hi) disease from the Pan American Health Organization (PAHO) and its five regional reference laboratories in South America, USA, and Canada in Ottawa, Ontario, Canada. This workshop built upon recommendations of previous related workshops and incorporated updated data.

R-Ras signals through specific integrin alpha cytoplasmic domains to promote migration and invasion of breast epithelial cells.

Specificity and modulation of integrin function have important consequences for cellular responses to the extracellular matrix, including differentiation and transformation. The Ras-related GTPase, R-Ras, modulates integrin affinity, but little is known of the signaling pathways and biological functions downstream of R-Ras. Here we show that stable expression of activated R-Ras or the closely related TC21 (R-Ras 2) induced integrin-mediated migration and invasion of breast epithelial cells through collagen and disrupted differentiation into tubule structures, whereas dominant negative R-Ras had opposite effects. These results imply novel roles for R-Ras and TC21 in promoting a transformed phenotype and in the basal migration and polarization of these cells. Importantly, R-Ras induced an increase in cellular adhesion and migration on collagen but not fibronectin, suggesting that R-Ras signals to specific integrins. This was further supported by experiments in which R-Ras enhanced the migration of cells expressing integrin chimeras containing the alpha2, but not the alpha5, cytoplasmic domain. In addition, a transdominant inhibition previously noted only between integrin beta cytoplasmic domains was observed for the alpha2 cytoplasmic domain; alpha2beta1-mediated migration was inhibited by the expression of excess alpha2 but not alpha5 cytoplasmic domain-containing chimeras, suggesting the existence of limiting factors that bind the integrin alpha subunit. Using pharmacological inhibitors, we found that R-Ras induced migration on collagen through a combination of phosphatidylinositol 3-kinase and protein kinase C, but not MAPK, which is distinct from the other Ras family members, Rac, Cdc42, and N- and K-Ras. Thus, R-Ras communicates with specific integrin alpha cytoplasmic domains through a unique combination of signaling pathways to promote cell migration and invasion.

R-Ras promotes apoptosis caused by growth factor deprivation via a Bcl-2 suppressible mechanism.

The Bcl-2 protein is an important regulator of programmed cell death, but the biochemical mechanism by which this protein prevents apoptosis remains enigmatic. Recently, Bcl-2 has been reported to physically interact with a member of the Ras superfamily of small GTPases, p23-R-Ras. To examine the functional significance of R-Ras for regulation of cell death pathways, the IL-3-dependent cells 32D.3 and FL5.12 were stably transfected with expression plasmids encoding an activated form (38 Glycine-->Valine) of R-Ras protein. R-Ras(38V)-producing 32D.3 and FL5.12 cells experienced increased rates of apoptotic cell death relative to control transfected cells when deprived of IL-3. Analysis of several independent clones of transfected 32D.3 cells revealed a correlation between higher levels of R-Ras protein and faster rates of cell death upon withdrawal of IL-3 from cultures. 32D.3 cells cotransfected with R-Ras(38V) and Bcl-2 exhibited prolonged cell survival in the absence of IL-3, equivalent to 32D.3 cells transfected with Bcl-2 expression plasmids alone. R-Ras(38V) also increased rates of cell death in serum-deprived NIH-3T3 cells, and Bcl-2 again abrogated most of this effect. The ratio of GTP and GDP bound to R-Ras(38V) was not significantly different in control 32D.3 cells vs those that overexpressed Bcl-2, indicating that Bcl-2 does not abrogate R-Ras-mediated effects on cell death by altering R-Ras GDP/GTP regulation. Moreover, purified Bcl-2 protein had no effect on the GTPase activity of recombinant wild-type R-Ras in vitro. When expressed in Sf9 cells using recombinant baculoviruses, R-Ras(38V) bound to and induced activation of Raf-1 kinase irrespective of whether Bcl-2 was coproduced in these cells, suggesting that Bcl-2 does not nullify R-Ras effects by interfering with R-Ras-mediated activation of Raf-1 kinase. Taken together, these findings suggest that R-Ras enhances the activity of a cell death pathway in growth factor-deprived cells and imply that Bcl-2 acts downstream of R-Ras to promote cell survival.

Rab1b regulates vesicular transport between the endoplasmic reticulum and successive Golgi compartments.

We report an essential role for the ras-related small GTP-binding protein rab1b in vesicular transport in mammalian cells. mAbs detect rab1b in both the ER and Golgi compartments. Using an assay which reconstitutes transport between the ER and the cis-Golgi compartment, we find that rab1b is required during an initial step in export of protein from the ER. In addition, it is also required for transport of protein between successive cis- and medial-Golgi compartments. We suggest that rab1b may provide a common link between upstream and downstream components of the vesicular fission and fusion machinery functioning in early compartments of the secretory pathway.

Angiotensin II stimulates calcium-dependent activation of c-Jun N-terminal kinase.

In GN4 rat liver epithelial cells, angiotensin II (Ang II) and other agonists which activate phospholipase C stimulate tyrosine kinase activity in a calcium-dependent, protein kinase C (PKC)-independent manner. Since Ang II also produces a proliferative response in these cells, we investigated downstream signaling elements traditionally linked to growth control by tyrosine kinases. First, Ang II, like epidermal growth factor (EGF), stimulated AP-1 binding activity in a PKC-independent manner. Because increases in AP-1 can reflect induction of c-Jun and c-Fos, we examined the activity of the mitogen-activated protein (MAP) kinase family members Erk-1 and -2 and the c-Jun N-terminal kinase (JNK), which are known to influence c-Jun and c-Fos transcription. Ang II stimulated MAP kinase (MAPK) activity but only approximately 50% as effectively as EGF; again, these effects were independent of PKC. Ang II also produced a 50- to 200-fold activation of JNK in a PKC-independent manner. Unlike its smaller effect on MAPK, Ang II was approximately four- to sixfold more potent in activating JNK than EGF was. Although others had reported a lack of calcium ionophore-stimulated JNK activity in lymphocytes and several other cell lines, we examined the role of calcium in GN4 cells. The following results suggest that JNK activation in rat liver epithelial cells is at least partially Ca(2+) dependent: (i) norepinephrine and vasopressin hormones that increase inositol 1,4,5-triphosphate stimulated JNK; (ii) both thapsigargin, a compound that produces an intracellular Ca(2+) signal, and Ca(2+) ionophores stimulated a dramatic increase in JNK activity (up to 200-fold); (iii) extracellular Ca(2+) chelation with ethylene glycol tetraacetic acid (EGTA) inhibited JNK activation by ionophore and intracellular chelation with 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl-ester (BAPTA-AM) partially inhibited JNK activation by Ang II or thapsigargin; and (iv) JNK activation by Ang II was inhibited by pretreatment of cells with thapsigargin and EGTA, a procedure which depletes intracellular Ca(2+) stores. JNK activation following Ang II stimulation did not involve calmodulin; either W-7 nor calmidizolium, in concentrations sufficient to inhibit Ca(2+)/calmodulin-dependent kinase II, blocked JNK activation by Ang II. In contrast, genistein, in concentrations sufficient to inhibit Ca(2+)-dependent tyrosine phosphorylation, prevented Ang II and thapsigargin-induced JNK activation. In summary, in GN4 rat liver epithelial cells, Ang II stimulates JNK via a novel Ca(2+)-dependent pathway. The inhibition by genistein suggest that Ca(2+)-dependent tyrosine phosphorylation may modulate the JNK pathway in a cell type-specific manner, particularly in cells with a readily detectable Ca(2+)-regulated tyrosine kinase.

Specific isoprenoid modification is required for function of normal, but not oncogenic, Ras protein.

While the Ras C-terminal CAAX sequence signals modification by a 15-carbon farnesyl isoprenoid, the majority of isoprenylated proteins in mammalian cells are modified instead by a 20-carbon geranylgeranyl moiety. To determine the structural and functional basis for modification of proteins by a specific isoprenoid group, we have generated chimeric Ras proteins containing C-terminal CAAX sequences (CVLL and CAIL) from geranylgeranyl-modified proteins and a chimeric Krev-1 protein containing the H-Ras C-terminal CAAX sequence (CVLS). Our results demonstrate that both oncogenic Ras transforming activity and Krev-1 antagonism of Ras transforming activity can be promoted by either farnesyl or geranylgeranyl modification. Similarly, geranylgeranyl-modified normal Ras [Ras(WT)CVLL], when overexpressed, exhibited the same level of transforming activity as the authentic farnesyl-modified normal Ras protein. Therefore, farnesyl and geranylgeranyl moieties are functionally interchangeable for these biological activities. In contrast, expression of moderate levels of geranylgeranyl-modified normal Ras inhibited the growth of untransformed NIH 3T3 cells. This growth inhibition was overcome by coexpression of the mutant protein with oncogenic Ras or Raf, but not with oncogenic Src or normal Ras. The similar growth-inhibiting activities of Ras(WT)CVLL and the previously described Ras(17N) dominant inhibitory mutant suggest that geranylgeranyl-modified normal Ras may exert its growth-inhibiting action by perturbing endogenous Ras function. These results suggest that normal Ras function may specifically require protein modification by a farnesyl, but not a geranylgeranyl, isoprenoid.

Aberrant function of the Ras-related protein TC21/R-Ras2 triggers malignant transformation.

Although the human Ras proteins are members of a large superfamily of Ras-related proteins, to date, only the proteins encoded by the three mammalian ras genes have been found to possess oncogenic potential. Among the known Ras-related proteins, TC21/R-Ras2 exhibits the most significant amino acid identity (55%) to Ras proteins. We have generated mutant forms of TC21 that possess amino acid substitutions analogous to those that activate Ras oncogenic potential [designated TC21(22V) and TC21(71L)] and compared the biological properties of TC21 with those of Ras proteins in NIH 3T3 and Rat-1 transformation assays. Whereas wild-type TC21 did not show any transforming potential in vitro, both TC21(22V) and TC21(71L) displayed surprisingly potent transforming activities that were comparable to the strong transforming activity of oncogenic Ras proteins. Like Ras-transformed cells, NIH 3T3 cells expressing mutant TC21 proteins formed foci of morphologically transformed cells in monolayer cultures, proliferated in low serum, formed colonies in soft agar, and developed progressive tumors in nude mice. Thus, TC21 is the first Ras-related protein to exhibit potent transforming activity equivalent to that of Ras. Furthermore, mutant TC21 proteins also stimulated constitutive activation of mitogen-activated protein kinases as well as transcriptional activation from Ras-responsive promoter elements (Ets/AP-1 and NF-kappa B). We conclude that aberrant TC21 function may trigger cellular transformation via a signal transduction pathway similar to that of oncogenic Ras and suggest that deregulated TC21 activity may contribute significantly to human oncogenesis.

TC21 causes transformation by Raf-independent signaling pathways.

Although the Ras-related protein TC21/R-Ras2 has only 55% amino acid identity with Ras proteins, mutated forms of TC21 exhibit the same potent transforming activity as constitutively activated forms of Ras. Therefore, like Ras, TC21 may activate signaling pathways that control normal cell growth and differentiation. To address this possibility, we determined if regulators and effectors of Ras are also important for controlling TC21 activity. First, we determined that Ras guanine nucleotide exchange factors (SOS1 and RasGRF/CDC25) synergistically enhanced wild-type TC21 activity in vivo and that Ras GTPase-activating proteins (GAPs; p120-GAP and NF1-GAP) stimulated wild-type TC21 GTP hydrolysis in vitro. Thus, extracellular signals that activate Ras via SOS1 activation may cause coordinate activation of Ras and TC21. Second, we determined if Raf kinases were effectors for TC21 transformation. Unexpectedly, yeast two-hybrid binding analyses showed that although both Ras and TC21 could interact with the isolated Ras-binding domain of Raf-1, only Ras interacted with full-length Raf-1, A-Raf, or B-Raf. Consistent with this observation, we found that Ras- but not TC21-transformed NIH 3T3 cells possessed constitutively elevated Raf-1 and B-Raf kinase activity. Thus, Raf kinases are effectors for Ras, but not TC21, signaling and transformation. We conclude that common upstream signals cause activation of Ras and TC21, but activated TC21 controls cell growth via distinct Raf-independent downstream signaling pathways.

The emerging Haemophilus influenzae serotype a infection and a potential vaccine: Implementation science in action.

Haemophilus influenzae serotype b (Hib) was a major cause of meningitis in children until Hib conjugate vaccine was introduced into the routine infant immunization program and Hib disease in children was almost eliminated. In Alaska, northern Canada and other countries with Indigenous peoples, H. influenzae serotype a (Hia) has emerged as a significant cause of pneumonia, meningitis and septic arthritis especially in children under 24 months of age. A joint government initiative between the Public Health Agency of Canada (PHAC) and the National Research Council of Canada (NRC) was carried out to assess whether an Hia vaccine could be developed for the common good. The initiative included strategic partnerships with clinician researchers in Thunder Bay, Ontario who provide health services to Indigenous people and the Artic Investigations Program (AIP) of the United States Centers for Disease Control and Prevention (CDC) in Alaska. This government initiated and funded research identified that the development of an Hia vaccine is possible and ongoing surveillance that includes strain characterization is essential to understand the potential spread of Hia in North America and around the world.

Developing a vaccine for Haemophilus influenzae serotype a: Proceedings of a workshop.

Since the late 1990s there has been an emergence of Haemophilus influenzae serotype a (Hia) infections, especially in Indigenous communities in the northern regions of Canada and Alaska associated with significant morbidity and approximately a 10% mortality. A Hia vaccine could potentially prevent this disease and save the health care system millions of dollars in both acute and long-term care. On March 23-24, 2016, the National Research Council (NRC), the Public Health Agency of Canada (PHAC) and the Canadian Institutes of Health Research (CIHR) co-organized a meeting on H. influenzae serotype a (Hia) to examine the current state of disease epidemiology and a potential vaccine solution path. The meeting included representatives from academia, federal and territorial public health units, hospital laboratories, federal departments involved in Aboriginal health, advocacy organizations for Indigenous peoples and industry. Representatives from industry confirmed having the capacity and the interest to support preparation of clinical trial batches. Canadian regulatory authorities have expressed a willingness to help ensure appropriate measures are in place for licensure purposes. Furthermore, there is the capacity and interest in performing some clinical trials in Indigenous communities in both Canada and Alaska. Recommendations for next steps included: complete pre-clinical studies, improve epidemiological surveillance to better understand the extent of the disease in the rest of North America and globally, establish engagement mechanisms with national Indigenous organizations to ensure their peoples are fully involved in the process and explore funding opportunities to prepare clinical lots and undertake clinical trials.

INO80 is required for oncogenic transcription and tumor growth in non-small cell lung cancer.

Epigenetic regulators are attractive targets for the development of new cancer therapies. Among them, the ATP-dependent chromatin remodeling complexes control the chromatin architecture and have important roles in gene regulation. They are often found to be mutated and de-regulated in cancers, but how they influence the cancer gene expression program during cancer initiation and progression is not fully understood. Here we show that the INO80 chromatin remodeling complex is required for oncogenic transcription and tumor growth in non-small-cell lung cancer (NSCLC). Ino80, the SWI/SNF ATPase in the complex, is highly expressed in NSCLC cells compared with normal lung epithelia cells. Further, its expression, as well as that of another subunit Ino80B, negatively correlates with disease prognosis in lung cancer patients. Functionally, INO80 silencing inhibits NSCLC cell proliferation and anchorage-independent growth in vitro and tumor formation in mouse xenografts. It occupies enhancer regions near lung cancer-associated genes, and its occupancy correlates with increased genome accessibility and enhanced expression of downstream genes. Together, our study defines a critical role of INO80 in promoting oncogenic transcription and NSCLC tumorigenesis, and reveals a potential treatment strategy for inhibiting the cancer transcription network by targeting the INO80 chromatin remodeling complex.

First characterization of immunogenic conjugates of Vi negative Salmonella Typhi O-specific polysaccharides with rEPA protein for vaccine development.

Efficacious typhoid vaccines for young children will significantly reduce the disease burden in developing world. The Vi polysaccharide based conjugate vaccines (Vi-rEPA) against Salmonella Typhi Vi positive strains has shown high efficacy but may be ineffective against Vi negative S. Typhi. In this study, for the first time, we report the synthesis and evaluation of polysaccharide-protein conjugates of Vi negative S. Typhi as potential vaccine candidates. Four different conjugates were synthesized using recombinant exoprotein A of Pseudomonas aeruginosa (rEPA) and human serum albumin (HSA) as the carrier proteins, using either direct reductive amination or an intermediate linker molecule, adipic acid dihydrazide (ADH). Upon injection into mice, a significantly higher antibody titer was observed in mice administrated with conjugate-1 (OSP-HSA) (P=0.0001) and conjugate 2 (OSP-rEPA) (P≤0.0001) as compared to OSP alone. In contrast, the antibody titer elicited by conjugate 3 (OSPADH-HSA) and conjugate 4 (OSPADH-rEPA) were insignificant (P=0.1684 and P=0.3794, respectively). We conclude that reductive amination is the superior method to prepare the S. Typhi OSP glycoconjugate. Moreover, rEPA was a better carrier protein than HSA. Thus OSP-rEPA conjugate seems to be efficacious typhoid vaccines candidate, it may be evaluated further and recommended for the clinical trials.

The farnesyltransferase inhibitor FTI-277 radiosensitizes H-ras-transformed rat embryo fibroblasts.

Many tumor cells have a greater resistance to ionizing radiation than their normal counterparts, suggesting that the development of drugs that can reduce that radioresistance would potentiate the efficacy of radiation therapy. Because activated H-ras expression has been shown to markedly increase radiation resistance in some transformed cells, the inactivation of H-ras would then be predicted to radiosensitize these tumor cells, while leaving normal cells unaffected. H-ras depends for activity upon farnesylation, which can be blocked by farnesylation inhibitors, including the compound FTI-277. In keeping with this prediction, inhibition of H-ras processing using FTI-277 resulted in higher levels of apoptosis after irradiation and increased radiosensitivity in H-ras-transformed rat embryo cells but did not affect control cells. These experiments suggest that farnesylation inhibitors may prove clinically useful as radiosensitizers of tumors that depend on ras function.

R-Ras is regulated by activators and effectors distinct from those that control Ras function.

Like Ras, constitutively activated mutants of the Ras-related protein R-Ras cause tumorigenic transformation of NIH3T3 cells. However, since R-Ras causes a transformed phenotype distinct from that induced by Ras, it is likely that R-Ras controls signaling pathways and cellular processes distinct from those regulated by Ras. To address this possibility, we determined if R-Ras is regulated by activators and effectors distinct from those that regulate Ras function. We observed that Ras guanine nucleotide exchange factors failed to activate R-Ras in vivo, indicating that R-Ras is activated by distinct GEFs. Consistent with this, mutants of R-Ras with mutations analogous to the Ras(15A)/(17N) dominant negative proteins did not antagonize Ras GEF function and lacked the growth inhibitory activity seen with these mutant Ras proteins. Thus, R-Ras, but not Ras, is dispensable for the viability of NIH3T3 cells. Finally, whereas constitutively activated Ras can overcome the growth inhibitory action of the Ras(17N) dominant negative protein via Raf-dependent and -independent activities, transforming mutants of R-Ras failed to do so. This inability was consistent with our observation that Ras-, but not R-Ras-transformed, NIH3T3 cells possessed constitutively upregulated Raf kinase activities. Thus, R-Ras and Ras are regulators of distinct signaling pathways and cellular processes.

R-Ras induces malignant, but not morphologic, transformation of NIH3T3 cells.

Although previous studies have not identified transforming properties of the Ras-related protein R-Ras, two recent observations have prompted our further evaluation of R-Ras function. First, we observed that mutant forms of the closely related R-Ras2/TC21 protein (approximately 70% identity) exhibited the same potent transforming activity as oncogenic Ras proteins. Second, R-Ras association with Bcl-2 suggested a possible role for R-Ras in apoptotic growth control. Therefore, we have performed a detailed analysis of R-Ras transforming potential in NIH3T3 cells. Whereas expression of a mutant R-Ras protein (38V; analogous to the 12V activating Ras mutation) did not induce morphologic transformation of NIH3T3 cells, R-Ras(38V)-expressing cells proliferated in low serum, formed colonies in soft agar, and formed progressive tumors in nude mice. Like Ras-transformed cells, R-Ras(38V)-transformed cells exhibited constitutively activated mitogen activated protein kinases. Furthermore, R-Ras(38V) stimulated transcriptional activation of Ras-responsive promoter elements, and this activity (and transformation) was blocked by Raf dominant negative proteins. Finally, whereas co-expression of Bcl-2 did not cause significant alteration in wild type or mutant R-Ras transforming activity, coexpression of v-Myc and R-Ras(38V) induced a striking morphologic transformation of NIH3T3 cells. Taken together, these observations suggest that aberrant R-Ras function may stimulate malignant transformation, in the absence of morphologic transformation, via up-regulation of part of the Ras signal transduction pathway.

Novel determinants of H-Ras plasma membrane localization and transformation.

Although it is well-established that modification of Ras by farnesol is a critical step for its membrane association and transforming activity, the contribution of other C-terminal sequences and palmitate modification to Ras localization and function remains unclear. We have characterized H-Ras mutant proteins with alterations in the palmitoylated cysteines or in sequences flanking these residues. We found that non-palmitoylated proteins were impaired not only in membrane association but also in transforming activity. Mutations which drastically altered residues adjacent to the palmitoylated cysteine did not abolish palmitoylation. However, despite continued lipid modification the mutant proteins failed to bind to plasma membranes and instead accumulated on internal membranes and, importantly, were not transforming. Addition of an N-terminal myristoylation signal to these defective mutants, or to proteins entirely lacking the C-terminal 25 residues restored both plasma membrane association and transforming activity. Thus, H-Ras does not absolutely require prenylation or palmitoylation nor indeed its hypervariable domain in order to interact with effectors that ultimately cause transformation. However, in this native state, the C-terminus appears to provide a combination of lipids and a previously unrecognized signal for specific plasma membrane targeting that are essential for the correct localization and biological function of H-Ras.

Ras, but not Src, transformation of RIE-1 epithelial cells is dependent on activation of the mitogen-activated protein kinase cascade.

Src transformation of NIH3T3 mouse fibroblasts has been shown to be dependent on Ras function. Since we recently showed that the signaling pathways that mediate Ras transformation of RIE-1 rat intestinal epithelial cells are distinct from those that cause Ras transformation of fibroblasts, we utilized three approaches to determine if Src transformation of RIE-1 cells is dependent on Ras. First, although both Ras and Src cause upregulation of an epidermal growth factor (EGF) receptor-dependent autocrine growth loop, only Ras transformation required this activity. Second, whereas both Src and Ras caused upregulation of the p42 and p44 mitogen-activated protein kinases (MAPKs), only Ras transformation was blocked by the inhibition of MAPK activation by treatment with the PD 98059 MEK inhibitor. Third, treatment with the farnesyltransferase inhibitor FTI-277 blocked Ras, but not Src, transformation. Taken together, these observations suggest that Src transformation of RIE-1 cells is not dependent on Ras. Finally, we determined that Ras activation of Raf-independent pathways alone is sufficient to cause growth transformation of RIE-1 cells. Thus, both Ras and Src cause transformation of RIE-1 cells via pathways distinct from those required to cause transformation of NIH3T3 cells.