Tissue-specific expression of rat c-ros-1 gene and partial structural similarity of its predicted products with sev protein of Drosophila melanogaster

Pre-clinical modelling of ROS1+ non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a heterogeneous group of diseases which accounts for 80% of newly diagnosed lung cancers. In the previous decade, a new molecular subset of NSCLC patients (around 2%) harboring rearrangements of the c-ros oncogene 1 was defined. ROS1+ NSCLC is typically diagnosed in young, nonsmoker individuals presenting an adenocarcinoma histology. Patients can benefit from tyrosine kinase inhibitors (TKIs) such as crizotinib and entrectinib, compounds initially approved to treat ALK-, MET- or NTRK- rearranged malignancies respectively. Given the low prevalence of ROS1-rearranged tumors, the use of TKIs was authorized based on pre-clinical evidence using limited experimental models, followed by basket clinical trials. After initiating targeted therapy, disease relapse is reported in approximately 50% of cases as a result of the appearance of resistance mechanisms. The restricted availability of TKIs active against resistance events critically reduces the overall survival. In this review we discuss the pre-clinical ROS1+ NSCLC models developed up to date, highlighting their strengths and limitations with respect to the unmet clinical needs. By combining gene-editing tools and novel cell culture approaches, newly developed pre-clinical models will enhance the development of next-generation tyrosine kinase inhibitors that overcome resistant tumor cell subpopulations.

ROS1-positive non-small cell lung cancer (NSCLC): biology, diagnostics, therapeutics and resistance

ROS1 is a proto-oncogene encoding a receptor tyrosine protein kinase (RTK), homologous to the v - Ros sequence of University of Manchester tumours virus 2 (UR2) sarcoma virus, whose ligands are still being investigated. ROS1 fusion genes have been identified in various types of tumours. As an oncoprotein, it promotes cell proliferation, activation and cell cycle progression by activating downstream signalling pathways, accelerating the development and progression of non-small cell lung cancer (NSCLC). Studies have demonstrated that ROS1 inhibitors are effective in patients with ROS1-positive NSCLC and are used for first-line clinical treatment. These small molecule inhibitors provide a rational therapeutic option for the treatment of ROS1-positive patients. Inevitably, ROS1 inhibitor resistance mutations occur, leading to tumours recurrence or progression. Here, we comprehensively review the identified biological properties and Differential subcellular localisation of ROS1 fusion oncoprotein promotes tumours progression. We summarise recently completed and ongoing clinical trials of the classic and new ROS1 inhibitors. More importantly, we classify the complex evolving tumours cell resistance mechanisms. This review contributes to our understanding of the biological properties of ROS1 and current therapeutic advances and resistant tumours cells, and the future directions to develop ROS1 inhibitors with durable effects.

ROS1-dependent cancers - biology, diagnostics and therapeutics

The proto-oncogene ROS1 encodes a receptor tyrosine kinase with an unknown physiological role in humans. Somatic chromosomal fusions involving ROS1 produce chimeric oncoproteins that drive a diverse range of cancers in adult and paediatric patients. ROS1-directed tyrosine kinase inhibitors (TKIs) are therapeutically active against these cancers, although only early-generation multikinase inhibitors have been granted regulatory approval, specifically for the treatment of ROS1 fusion-positive non-small-cell lung cancers; histology-agnostic approvals have yet to be granted. Intrinsic or extrinsic mechanisms of resistance to ROS1 TKIs can emerge in patients. Potential factors that influence resistance acquisition include the subcellular localization of the particular ROS1 oncoprotein and the TKI properties such as the preferential kinase conformation engaged and the spectrum of targets beyond ROS1. Importantly, the polyclonal nature of resistance remains underexplored. Higher-affinity next-generation ROS1 TKIs developed to have improved intracranial activity and to mitigate ROS1-intrinsic resistance mechanisms have demonstrated clinical efficacy in these regards, thus highlighting the utility of sequential ROS1 TKI therapy. Selective ROS1 inhibitors have yet to be developed, and thus the specific adverse effects of ROS1 inhibition cannot be deconvoluted from the toxicity profiles of the available multikinase inhibitors. Herein, we discuss the non-malignant and malignant biology of ROS1, the diagnostic challenges that ROS1 fusions present and the strategies to target ROS1 fusion proteins in both treatment-naive and acquired-resistance settings.

ROS-dependent DNA damage contributes to crizotinib-induced hepatotoxicity via the apoptotic pathway

Crizotinib is an oral small-molecule tyrosine kinase inhibitor targeting anaplastic lymphoma kinase (ALK), ROS proto-oncogene 1, receptor tyrosine kinase (ROS1) and MET proto-oncogene, receptor tyrosine kinase (MET). Unfortunately, hepatotoxicity is a serious limitation in its clinical application, and the reason remains largely unknown. In this study, we tested the effect of crizotinib in human hepatocyte cell line HL-7702 and human primary hepatocytes, and the results showed that crizotinib treatment caused hepatocyte damage, suggesting that crizotinib induced liver injury by causing hepatocyte death, consistent with the clinical cases. Mechanistically, crizotinib induced hepatocyte death via the apoptotic pathway, and cleaved PARP (c-PARP) was observed as a signaling protein. Moreover, mitochondrial membrane potential (MMP) decrease contributed to crizotinib-induced hepatocyte apoptosis accompanied by hepatocyte DNA damage and reactive oxygen species (ROS) generation. Importantly, crizotinib induced hepatocyte apoptosis independent of its targets, ALK, ROS1 and MET. In conclusion, our data showed that crizotinib induced liver injury through hepatocyte death via the apoptotic pathway which was independent of ALK, ROS1 and MET. And we also found that MMP decrease, DNA damage and ROS generation were involved in the process.

The ALK receptor in sympathetic neuron development and neuroblastoma

The ALK gene encodes a tyrosine kinase receptor characterized by an expression pattern mainly restricted to the developing central and peripheral nervous systems. In 2008, the discovery of ALK activating mutations in neuroblastoma, a tumor of the sympathetic nervous system, represented a breakthrough in the understanding of the pathogenesis of this pediatric cancer and established mutated ALK as a tractable therapeutic target for precision medicine. Subsequent studies addressed the identity of ALK ligands, as well as its physiological function in the sympathoadrenal lineage, its role in neuroblastoma development and the signaling pathways triggered by mutated ALK. This review focuses on these different aspects of the ALK biology and summarizes the various therapeutic strategies relying on ALK inhibition in neuroblastoma, either as monotherapies or combinatory treatments.

ROS1 signaling regulates epithelial differentiation in the epididymis

The initial segment (IS) of the epididymis plays an essential role in male fertility. The IS epithelium is undifferentiated and nonfunctional at birth. Prior to puberty, the epithelium undergoes differentiation that leads to the formation of a fully functional organ. However, the mechanistic details of this program are not well understood. To explore this further, we used genetic engineering to create a kinase dead allele of the ROS1 receptor tyrosine kinase in mice and studied the effects of ROS1 tyrosine kinase activity on the differentiation of the IS epithelium. We show that the expression and activation of ROS1 coincides with the onset of differentiation and is exclusively located in the IS of the maturing and adult mouse epididymides. Here we demonstrate that the differentiation of the IS is dependent on the kinase activity of ROS1 and its downstream effector MEK1/2-ERK1/2 signaling axis. Using genetic engineering, we show that germ line ablation of ROS1 kinase activity leads to a failure of the IS epithelium to differentiate, and as a consequence sperm maturation and infertility were dramatically perturbed. Pharmacological inhibition of ROS1 kinase activity in the developing epididymis, however, only delayed differentiation transiently and did not result in infertility. Our results demonstrate that ROS1 kinase activity and the ensuing MEK1/2-ERK1/2 signaling are necessary for the postnatal development of the IS epithelium and that a sustained ablation of ROS1 kinase activity within the critical window of terminal differentiation abrogate the function of the epididymis and leads to sterility.

ROS receptor tyrosine kinase: a new potential target for anticancer drugs

ROS kinase is one of the last two remaining orphan receptor tyrosine kinases with an as yet unidentified ligand. The normal functions of human ROS kinase in different body tissues have not been fully identified so far. However, the ectopic expression, as well as the production of variable mutant forms of ROS kinase has been reported in a number of cancers, such as glioblastoma multiforme, and non-small cell lung cancer, suggesting a role for ROS kinase in deriving such tumors. It is thought also that c-ROS gene may have a role in some cardiovascular diseases, and the fact that homozygous male mice targeted against c-ROS gene are healthy but infertile, has inspired researchers to think about ROS inhibition as a method for development of new male contraceptives. The recent discovery of new selective and potent inhibitors for ROS kinase, along with the development of new specific diagnostic methods for the detection of ROS fusion proteins, raises the importance of using these selective inhibitors for targeting ROS mutations as a new method for treatment of cancers harboring such genes. This review focuses on the ectopic expression of ROS and its fusion proteins in different cancer types and highlights the importance of targeting these proteins for treatment of substantial cancers. It describes also the recent advances in the field of ROS kinase inhibition, and the potential clinical applications of ROS kinase inhibitors.

The multifaceted roles of the receptor tyrosine kinase ROS in development and cancer

The proto-oncogene receptor tyrosine kinase ROS was originally discovered through the identification of oncogenic variants isolated from tumors. These discoveries spearheaded a body of work aimed at elucidating the function of this evolutionarily conserved receptor in development and cancer. Through genetic and biochemical approaches, progress in the characterization of ROS points to distinctive roles in the program of epithelial cell differentiation during the development of a variety of organs. Although substantial, these advances remain hampered by the absence of an identified ligand, making ROS one of the last two remaining orphan receptor tyrosine kinases. Recent studies on the oncogenic activation of ROS as a result of different chromosomal rearrangements found in brain and lung cancers have shed light on the molecular mechanisms underlying ROS transforming activities. ROS and its oncogenic variants therefore constitute clinically relevant targets for cancer therapeutic intervention. This review highlights the various roles that this receptor plays in multiple system networks in normalcy and disease and points to future directions towards the elucidation of ROS function in the context of ligand identification, signaling pathways and clinical applications.

Novel hepatic progenitor cell surface markers in the adult rat liver

Hepatic progenitor/oval cells appear in injured livers when hepatocyte proliferation is impaired. These cells can differentiate into hepatocytes and cholangiocytes and could be useful for cell and gene therapy applications. In this work, we studied progenitor/oval cell surface markers in the liver of rats subjected to 2-acetylaminofluorene treatment followed by partial hepatectomy (2-AAF/PH) by using rat genome 230 2.0 Array chips and subsequent RT-PCR, immunofluorescent (IF), immunohistochemical (IHC) and in situ hybridization (ISH) analyses. We also studied expression of the identified novel cell surface markers in fetal rat liver progenitor cells and FAO-1 hepatoma cells. Novel cell surface markers in adult progenitor cells included tight junction proteins, integrins, cadherins, cell adhesion molecules, receptors, membrane channels and other transmembrane proteins. From the panel of 21 cell surface markers, 9 were overexpressed in fetal progenitor cells, 6 in FAO-1 cells and 6 are unique for the adult progenitors (CD133, claudin-7, cadherin 22, mucin-1, ros-1, Gabrp). The specificity of progenitor/oval cell surface markers was confirmed by ISH and double IF analyses. Moreover, study of progenitor cells purified with Ep-CAM antibodies from D-galactosamine injured rat liver, a noncarcinogenic model of progenitor cell activation, verified that progenitor cells expressed these markers.

CONCLUSION

We identified novel cell surface markers specific for hepatic progenitor/oval cells, which offers powerful tool for their identification, isolation and studies of their physiology and pathophysiology. Our studies also reveal the mesenchymal/epithelial phenotype of these cells and the existence of species diversity in the hepatic progenitor cell identity.

Technologies for the study of epididymal-specific genes

Sperm maturation occurs during transit through the epididymis. Interactions between the epididymal epithelium and the sperm are crucial for the maturation process. Analyses of existing male-infertile mouse lines have begun to enumerate some of the genes involved. Recent advances in transgenic technologies to generate temporally and spatially restricted targeted gene disruptions show promise for progress in understanding sperm maturation. Gene silencing agents, such as RNAi, to manipulate gene expression may prove useful for the analysis of epididymal genes involved in the maturation process.

Matrix-independent activation of phosphatidylinositol 3-kinase, Stat3, and cyclin A-associated Cdk2 Is essential for anchorage-independent growth of v-Ros-transformed chicken embryo fibroblasts

The question remains open whether the signaling pathways shown to be important for growth and transformation in adherent cultures proceed similarly and play similar roles for cells grown under anchorage-independent conditions. Chicken embryo fibroblasts (CEF) infected with the avian sarcoma virus UR2, encoding the oncogenic receptor protein-tyrosine kinase (RPTK) v-Ros, or with two of its transformation-impaired mutants were grown in nonadherent conditions in methylcellulose (MC)-containing medium, and the signaling functions essential for Ros-induced anchorage-independent growth were analyzed. We found that the overall tyrosine phosphorylation of cellular proteins in CEF transformed by v-Ros or by two oncogenic nonreceptor protein-tyrosine kinases (PTKs), v-Src and v-Yes, was dramatically reduced in nonadherent conditions compared with that in adherent conditions, indicating that cell adhesion to the extracellular matrix plays an important role in efficient substrate phosphorylation by these constitutively activated PTKs. The UR2 transformation-defective mutants were differentially impaired compared with UR2 in the activation of phosphatidylinositol 3-kinase (PI 3-kinase) and Stat3 in nonadherent conditions. Consistently, the constitutively activated mutants of PI 3-kinase and Stat3 rescued the ability of the UR2 mutants to promote anchorage-independent growth. Conversely, dominant negative mutants of PI 3-kinase and Stat3 inhibited UR2-induced anchorage-independent growth. UR2-infected CEF grown in nonadherent conditions displayed faster cell cycle progression than the control or the UR2 mutant-infected cells, and this appeared to correlate with a PI 3-kinase-dependent increase in cyclin A-associated Cdk2 activity. Treatment of UR2-infected cells with Cdk2 inhibitors led to the loss of the anchorage-independent growth-promoting activity of UR2. In conclusion, we have adopted an experimental system enabling us to study the signaling pathways in cells grown under anchorage-independent conditions and have identified matrix-independent activation of PI 3-kinase and Stat3 signaling functions, as well as the PI 3-kinase-dependent increase of cyclin A-associated Cdk2 kinase activity, to be critical for the Ros-PTK-induced anchorage-independent growth.

Involvement of receptor-type tyrosine kinase gene families in cardiac hypertrophy

OBJECTIVE

The activation of protein tyrosine kinases (PTKs) has been postulated to be involved in cell differentiation and proliferation. To elucidate the involvement of tyrosine kinase genes in normal and pathological conditions, we analysed the expression patterns of receptor-type PTKs in the normal and hypertensive hypertrophied heart in rats.

MATERIALS AND METHODS

Hypertrophied and normal rat hearts were obtained from hypertensive rats; deoxycorticosterone acetate (DOCA)-salt and 2 kidney-1 clip (2K-1C), and their sham-operated rats, respectively. A reverse transcription-polymerase chain reaction (RT-PCR) was performed using degenerated primers which were designed from highly conserved regions in the catalytic domains of receptor-type PTKs. The PCR products were ligated into a sequence vector, and subcloned by transforming bacteria. To compare the expression level of these PTK mRNAs in the normal and hypertrophied heart, we performed semi-competetive RT-PCR and immunohistochemical and Western blot analyses.

RESULTS

Nucleotide sequencing of approximately 80 clones of PTKs revealed 10 receptor-type, five nonreceptor-type and two unknown types in the rat heart. Tie-2/Tek, Ryk, insulin-like growth factor-I receptor were abundantly expressed in the rat heart as members of receptor-type PTKs. Immunohistochemistry and RT-PCR demonstrated the presence of platelet-derived growth factor (PDGF)-alpha receptor, PDGF-beta receptor and fibroblast growth factor-3 receptor in both normal and hypertrophied hearts. We also confirmed the presence of Flt-1, KDR/FIk-1, and their ligand vascular endothelial growth factor, c-Met and its ligand hepatocyte growth factor (HGF), and Tie-1, Tie-2/Tek by immunohistochemistry and RT-PCR. The coexpression of cardiac HGF and c-Met in hypertrophied hearts, especially in 2K-1 C rats, was induced more intensively than that in DOCA-salt rats.

CONCLUSION

These findings suggest that HGF/c-Met interactions may play an important role in cardiac hypertrophy and remodeling, probably as a result of the activation of the local renin-angiotensin system.

Genomic organization of the flt-1 gene encoding for vascular endothelial growth factor (VEGF) receptor-1 suggests an intimate evolutionary relationship between the 7-Ig and the 5-Ig tyrosine kinase receptors

The flt-1 tyrosine kinase gene encodes a high affinity receptor for Vascular Endothelial Growth Factor, and belongs to the so-called '7-Ig' or flt gene family which has characteristics of 7-Immunoglobulin (Ig)-like domains in the extracellular region. This is structurally distantly related to 5-Ig domain-containing receptors such as Fms/Kit/PDGF-R. However, the whole genomic organization for any 7-Ig receptor gene has not been determined yet. To examine the genomic structure of flt-1 and the evolutionary relationship between genes of the 7-Ig and 5-Ig receptor families, we isolated the mouse genomic DNAs carrying all exons of the flt-1 gene. The mouse flt-1 gene consisted of 30 exons, whose exon-intron boundaries were highly related to those in the 5-Ig receptor genes, except for the amino terminal region. The sequences corresponding to the first and second Ig-domains in the flt-1 gene were encoded by four exons, whereas this region was encoded by only two exons in the 5-Ig receptor genes. These results raise the interesting possibility that deletion or insertion mutations of introns in one of these receptor genes took place in the evolutionary generation of the other receptor genes.

Mutations of Ros differentially effecting signal transduction pathways leading to cell growth versus transformation

The signaling functions of the oncogenic protein-tyrosine kinase v-Ros were studied by systematically mutating the tyrosine residues in its cytoplasmic domain. The carboxyl mutation of Tyr-564 produces the most pronounced inhibitory effect on v-Ros autophosphorylation and interaction with phospholipase Cgamma. A cluster of 3 tyrosine residues, Tyr-414, Tyr-418, and Tyr-419, within the PTK domain of v-Ros plays an important role in modulating its kinase activity. The mutant F419 and the mutant DI, deleting 6-amino acids near the catalytic loop, retain wild type protein tyrosine kinase and mitogenic activities, but have dramatically reduced oncogenicity. Both mutant proteins are able to phosphorylate or activate components in the Ras/microtubule-associated protein kinase signaling pathway. However, F419 mutant protein is unable to phosphorylate insulin receptor substrate 1 (IRS-1) or promote association of IRS-1 with phosphatidylinositol 3-kinase. This tyrosine residue in the context of the NDYY motif may define a novel recognition site for IRS-1. Both F419 and DI mutants display impaired ability to induce tyrosine phosphorylation of a series of cytoskeletal and cell-cell interacting proteins. Thus the F419 and DI mutations define v-Ros sequences important for cytoskeleton signaling, the impairment of which correlates with the reduced cell transforming ability.

The c-ros tyrosine kinase receptor controls regionalization and differentiation of epithelial cells in the epididymis

The c-ros gene was originally identified in mutant form as an oncogene. The proto-oncogene encodes a tyrosine kinase receptor that is expressed in a small number of epithelial cell types, including those of the epididymis. Targeted mutations of c-ros in the mouse reveal an essential role of the gene in male fertility. Male c-ros -/- animals do not reproduce, whereas the fertility of female animals is not affected. We demonstrate that c-ros is not required in a cell autonomous manner for male germ cell development or function. The gene, therefore, does not affect sperm generation or function in a direct manner. The primary defect in the mutant animals was located in the epididymis, showing that c-ros controls appropriate development of the epithelia, particularly regionalization and terminal differentiation. The epididymal defect does not interfere with production or storage of sperm but, rather, with sperm maturation and the ability of sperm to fertilize in vivo. Interestingly, sperm isolated from c-ros -/- animals can fertilize in vitro. Our results highlight the essential role of the epididymis in male fertility and demonstrate a highly specific function of the c-ros receptor tyrosine kinase during development of distinct epithelial cells.

Two chimeric receptors of epidermal growth factor receptor and c-Ros that differ in their transmembrane domains have opposite effects on cell growth

Two chimeric receptors, ER1 and ER2, were constructed. ER1 contains the extracellular and transmembrane (TM) domains derived from epidermal growth factor receptor and the cytoplasmic domain from c-Ros; ER2 is identical to ER1 except that its TM domain is derived from c-Ros. Both chimeras can be activated by epidermal growth factor and are capable of activating or phosphorylating an array of cellular signaling proteins. Both chimeras promote colony formation in soft agar with about equal efficiency. Surprisingly, ER1 inhibits while ER2 stimulates cell growth on monolayer culture. Cell cycle analysis revealed that all phases, in particular the S and G2/M phases, of the cell cycle in ER1 cells were elongated whereas G1 phase of ER2 cells was shortened threefold. Comparison of signaling pathways mediated by the two chimeras revealed several differences. Several early signaling proteins are activated or phosphorylated to a higher extent in ER1 than in ER2 cells in response to epidermal growth factor. ER1 is less efficiently internalized and remains tyrosine phosphorylated for a longer time than ER2. However, phosphorylation of the 66-kDa She protein, activation of mitogen activated protein kinase, and induction of c-fos and c-jun occur either to a lesser extent or for a shorter time in ER1 cells. Cellular protein phosphorylation patterns are also different in ER1 and ER2 cells. In particular, a 190-kDa Shc-associated protein is tyrosine phosphorylated in ER2 but not in ER1 cells. Our results indicate that the TM domains have a profound effect on the signal transduction and biological activity of those chimeric receptors. The results also imply that sustained stimulation of ER1 due to its retarded internalization apparently triggers an inhibitory response that dominantly counteracts the receptor-mediated mitogenic signals. These two chimeras, expressed at similar levels in the same cell type but having opposite effects on cell growth, provide an ideal system to study the mechanism by which a protein tyrosine kinase inhibits cell growth.

Cloning of mouse c-ros renal cDNA, its role in development and relationship to extracellular matrix glycoproteins

Renal organogenesis ensues following reciprocal interactions between the uninduced metanephric mesenchyme and the ureteric bud. Conceivably, the presence of ligands or growth factors on a given cell type, and expression of receptors, including receptor proto-oncogenes, on the other cell type of different lineage would facilitate such epithelial-mesenchymal interactions. During these interactions, other macromolecules, such as extracellular matrix (ECM) proteins, present at the epithelial-mesenchymal surface, also play a role in the kidney morphogenesis. In this study the proto-oncogene, c-ros, was cloned and sequenced; its role in the metanephric development was examined, and correlated with the changes in the expression of ECM proteins. The mouse c-ros renal cDNA, belonging to phosphotyrosine kinase (PTK) receptor family, had a translation product of 2340 amino acids. The extracellular domain had 32 N-linked glycosylation sites and 30 cysteine residues. The transmembrane segment had a hydrophobicity approaching approximately 3.5. Multiple phosphorylation sites, typical of a PTK catalytic unit, were present in the cytoplasmic domain. The 3' noncoding region did not contain any A(U)nA mRNA instability motifs. The c-ros mRNA was highly expressed on the ureteric bud branches and their tips and on the developing glomeruli. Competitive RT-PCR analyses revealed the c-ros expression was the highest at 13th day of gestation, and it declined to very low levels during the neonatal period. Exposure of metanephric kidneys to c-ros antisense-oligonucleotide, derived from the PTK domain, caused dysmorphogenesis of the kidney and loss of c-ros expression on the ureteric bud branches. Concomitant with the reduced c-ros gene expression, a decreased expression of ECM glycoproteins, in particular the proteoglycans, was observed. These findings suggest that the c-ros plays a role in the metanephric development, and its effects may be modulated by the ECM macromolecules present at the epithelial-mesenchymal interface.

Expression of the ROS1 oncogene for tyrosine receptor kinase in adult human meningiomas

Oncogenes have been implicated in the promotion and progression of cancer in humans. Expression of the ROS1 oncogene, a member of the receptor tyrosine kinase superfamily, was examined in human meningiomas by coupled reverse transcription and polymerase chain reaction (RT-PCR) assays. Two sets of region-specific oligonucleotides, specific for different regions of the ROS1 messenger ribonucleic acid (mRNA), were used in RT-PCR assays to independently examine ROS1 transcripts from primary human meningiomas. ROS1 was expressed at high levels in approximately 55% (17 of 31) of the meningiomas examined, but not expressed in non-neoplastic brain samples. The commonplace expression of the ROS1 oncogene in meningiomas suggests a role for this oncogene in the etiology of these tumors.

A diversity of enzymes involved in the regulation of reversible tyrosine phosphorylation in sea urchin eggs and embryos

Reversible tyrosine phosphorylation is involved in the fertilization reaction and early embryogenesis of the sea urchin (Foltz and Shilling, 1993; Ramachandran et al., 1993). To determine the enzymes present that may be involved in this regulation, we used a PCR screen to identify sequences that encode protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP). We identified five PTKs and eight PTPs using cDNA libraries from two sea urchin species at two different stages of development, and the similarities to known PTK and PTP amino acid sequences ranged from 70 to 95%. The cognate proteins represented both "receptor"-class and cytoplasmic enzymes. Using RNAse protection assays we found that the respective mRNAs showed many accumulation profiles that we have grouped into three basic patterns: (1) mRNA levels that do not vary by more than two to three times throughout development; (2) mRNA levels highest in eggs or ovaries; and (3) mRNA levels highest in gastrula or pluteus stages. mRNAs specific to adult somatic cells of the ovary were not found, nor were mRNAs that accumulated selectively at the blastula stage. The results show that a diversity of enzymes involved in the regulation of reversible tyrosine phosphorylation is present in eggs and embryos of the sea urchin and that the differential accumulation in development of each mRNA suggests specific functional responsibilities by members of these enzyme families.

Modulatory effect of the transmembrane domain of the protein-tyrosine kinase encoded by oncogene ros: biological function and substrate interaction

There is a 3-aa insertion in the transmembrane (TM) domain of the p68gag-ros protein-tyrosine kinase encoded by avian sarcoma virus UR2 v-ros as compared with that of the protooncogene c-ros. The effect of this insertion on biological function and biochemical properties of v-Ros protein was investigated by deleting these 3 aa to generate the mutant TM1. This mutant has greatly reduced transforming, mitogenic, and tumorigenic activities despite the fact that the protein-tyrosine kinase activity and cell-surface localization of TM1 protein are unaffected. However, unlike UR2 protein, mutant TM1 protein becomes glycosylated, is differentially phosphorylated, and fails to induce tyrosine phosphorylation of a 88-kDa protein and a major substrate of insulin receptor, insulin receptor substrate 1. The TM1 protein is unable to associate with phosphatidylinositol 3-kinase and fails to promote association of insulin receptor substrate 1 with phosphatidylinositol 3-kinase. By contrast, tyrosine phosphorylation of Shc protein and phospholipase C gamma as well as interaction of Grb2 protein with Shc and SOS protein signaling components are unaltered in the TM1 infected cells. Our results show that the TM-domain sequence of p68gag-ros profoundly affects its function and substrate interaction. The mutant defines a signaling pathway including phosphatidylinositol 3-kinase, insulin receptor substrate 1, and possibly an 88-kDa protein that does not overlap the Ras pathway and is important for full transforming and mitogenic potency of v-ros protein-tyrosine kinase.

Oncogenes, Protein Tyrosine Kinases, and Signal Transduction

Many oncogenes encode protein tyrosine kinases (PTKs). Oncogenic mutations of these genes invariably result in constitutive activation of these PTKs. Autophosphorylation of the PTKs and tyrosine phosphorylation of their cellular substrates are essential events for transmission of the mitogenic signal into cells. The recent discovery of the characteristic amino acid sequences, of the src homology domains 2 and 3 (SH2 and SH3), and extensive studies on proteins containing the SH2 and SH3 domains have revealed that protein tyrosine-phosphorylation of PTKs provides phosphotyrosine sites for SH2 binding and allows extracellular signals to be relayed into the nucleus through a chain of protein-protein interactions mediated by the SH2 and SH3 domains. Studies on oncogenes, PTKs and SH2/SH3-containing proteins have made a tremendous contribution to our understanding of the mechanisms for the control of cell growth, oncogenesis, and signal transduction. This review is intended to provide an outline of the most recent progress in the study of signal transduction by PTKs. Copyright 1994 S. Karger AG, Basel

Molecular and biochemical bases for activation of the transforming potential of the proto-oncogene c-ros

The transforming gene of avian sarcoma virus UR2, v-ros, encodes a receptor-like protein tyrosine kinase and differs from its proto-oncogene, c-ros, in its 5' truncation and fusion to viral gag, a three-amino-acid (aa) insertion in the transmembrane (TM) domain, and changes in the carboxyl region. To explore the basis for activation of the c-ros transforming potential, various c-ros retroviral vectors containing those changes were constructed and studied for their biological and biochemical properties. Ufcros codes for the full-length c-ros protein of 2,311 aa, Uppcros has 1,661-aa internal deletion in the extracellular domain, CCros contains the 3' c-ros cDNA fused 150 aa upstream of the TM domain to the UR2 gag, CVros is the same as CCros except that the 3' region is replaced by that of v-ros, and VCros is the same as CCros except that the 5' region is replaced by that of v-ros. The Ufcros, Uppcros, CCros, and CVros are inactive in transforming chicken embryo fibroblasts, whereas VCros is as potent as UR2 in cell-transforming and tumorigenic activities. Upon passages of CCros and CVros viruses, the additional extracellular sequence in comparison with that of v-ros was delected; concurrently, both viruses (named CC5d and CV5d, respectively) attained moderate transforming activity, albeit significantly lower than that of UR2 or VCros. The native c-ros protein has a very low protein tyrosine kinase activity, whereas the ppcros protein is constitutively activated in kinase activity. The inability of CCros and CVros to transform chicken embryo fibroblasts is consistent with the inefficient membrane association, instability, and low kinase activity of their encoded proteins. The CC5d and CV5d proteins are indistinguishable in kinase activity, membrane association, and stability from the v-ros protein. The reduced transforming potency of CC5d and CV5d proteins can be attributed only to their differential substrate interaction, notably the failure to phosphorylate a 88-kDa protein. We conclude that the 5' rather than the 3' modification of c-ros is essential for its oncogenic activation; the sequence upstream of the TM domain has a negative effect on the transforming activity of CCros and CVros and needs to be deleted to activate their biological activity.

Tyrosine kinase receptors in the control of epithelial growth and morphogenesis during development

The c-ros, c-met and c-neu genes encode receptor-type tyrosine kinases and were originally identified because of their oncogenic potential. However, recent progress in the analysis of these receptors and their respective ligands indicate that they do not mediate exclusively mitogenic signals. Rather, they can induce cell movement, differentiation or morphogenesis of epithelial cells in culture. Interestingly, the discussed receptors are expressed in embryonal epithelia, whereas direct and indirect evidence shows that the corresponding ligands are produced in mesenchymal cells. In development, signals given by mesenchymal cells are major driving forces for differentiation and morphogenesis of epithelia; embryonal epithelia are generally unable to differentiate without the appropriate mesenchymal factors. The observed activities of these receptor/ligand systems in cultured cells and their expression patterns indicate that they regulate epithelial differentiation and morphogenesis also during embryogenesis and suggest thus a molecular basis for mesenchymal epithelial interactions.

A mouse c-ros genomic clone: identification of a highly conserved 22-amino acid segment in the juxta-membrane domain

The mouse c-ros protooncogene genomic sequences have been cloned; an analysis of the partial genomic clone revealed a high conservation of the exons encoding the juxta-membrane (JM) and the 5' most protein tyrosine kinase domains. We have identified a segment of 22 amino acids conserved between the human and mouse JM domains; this segment may have a critical role in the function of the c-ros-encoded protein tyrosine kinase receptor.

Enhancement of transforming potential of human insulinlike growth factor 1 receptor by N-terminal truncation and fusion to avian sarcoma virus UR2 gag sequence

The human insulinlike growth factor 1 (hIGF-1) receptor (hIGFR) is a transmembrane protein tyrosine kinase (PTK) molecule which shares high sequence homology in the PTK domain with the insulin receptor and, to a lesser degree, the ros transforming protein of avian sarcoma virus UR2. To assess the transforming potential of hIGFR, we introduced the intact and altered hIGFR into chicken embryo fibroblasts (CEF). The full-length hIGFR cDNA (fIGFR) was cloned into a UR2 retroviral vector, replacing the original oncogene v-ros. fIGFR was able to promote the growth of CEF in soft agar and cause morphological alteration in the absence of added hIGF-1 to medium containing 11% calf and 1% chicken serum. The transforming ability of hIGFR was not further increased in the presence of 10 nM exogenous hIGF-1. The 180-kDa protein precursor of hIGFR was synthesized and processed into alpha and beta subunits. The overexpressed hIGFR in CEF bound hIGF-1 with high affinity (Kd = 5.4 x 10(-9) M) and responded to ligand stimulation with increased tyrosine autophosphorylation. The cDNA sequence coding for part of the beta subunit of hIGFR, including 36 amino acids of the extracellular domain and the entire transmembrane and cytoplasmic domains, was fused to the 5' portion of the gag gene in the UR2 vector to form an avian retrovirus. The resulting virus, named UIGFR, was able to induce morphological transformation and promote colony formation of CEF with a stronger potency than did fIGFR. The UIGFR genome encodes a membrane-associated, glycosylated gag-IGFR fusion protein. The specific tyrosine phosphorylation of the mature form of the fusion protein, P75, is sixfold higher in vitro and threefold higher in vivo than that of the native IGFR beta subunit, P95. In conclusion, overexpression of the native or an altered hIGFR can induce transformation of CEF with the gag-IGFR fusion protein possessing enhanced transforming potential, which is consistent with its increased in vitro and in vivo tyrosine phosphorylation.

Two point mutations in the transmembrane domain of P68gag-ros inactive its transforming activity and cause a delay in membrane association

The transforming protein of the avian sarcoma virus UR2 is a 68-kDa transmembrane tyrosine protein kinase. We examined the relationship between membrane localization and transforming activity of P68 by changing Val-168-Val-169 in its hydrophobic domain into Asp-168-Glu-169. The resulting transmembrane (TM) mutant (P68TM) lost transforming activity toward chicken embryo fibroblasts (CEF). We found that the mutant protein was expressed and rapidly degraded into a smaller form which was still membrane associated and kinase active. The instability of the TM mutant protein is a phenomenon only manifested in CEF, because the same mutant protein was expressed with efficiency and stability similar to those of the wild-type protein in a transient expression system in COS cells. However, there are several differences between the wild-type and the TM mutant proteins in COS cells. The wild-type protein is more heavily phosphorylated and associated with membrane fractions in a cotranslational manner. It is enzymatically active when recovered from membrane fractions. The TM mutant protein is less phosphorylated, more labile toward protease degradation, and delayed in membrane association, with a lag period of 30 min or longer, and has little kinase activity when recovered from membrane fractions. Most of the kinase-active TM mutant protein was found in the cytosol fractions. Despite the delay, most of the TM protein in COS cells was found to be membrane associated, and its orientation on the cell surface was similar to that of the wild-type protein. It is probable that loss of the CEF-transforming activity of the TM mutant protein is due to its susceptibility to protease degradation resulting from improper membrane association of the newly synthesized product. The differences in the kinetics of membrane association and the distribution of kinase activity in COS cells might not be directly applicable in explaining the inability of the TM mutant to transform CEF but are intriguing as regards protein biosynthesis and translocation. The difference between CEF and COS cells implies that different factors or pathways are involved in the biosynthesis and processing of the TM mutant protein in these two cellular environments. Changes of P68TM in the kinetics of membrane association indicate that the transmembrane domain of ros, besides functioning as a membrane anchor, also plays a role in directing initial membrane association.

Comparison of the sevenless genes of Drosophila virilis and Drosophila melanogaster

The sevenless gene of Drosophila melanogaster encodes a transmembrane tyrosine kinase receptor required for normal eye development. We report here the isolation and DNA sequence analysis of the sevenless gene from Drosophila virilis. The predicted amino acid sequences of the sevenless proteins from these two species, which diverged approximately 60 million years ago, are compared.

Structure and function of the protein tyrosine kinases

The protein tyrosine kinases (PTKs) are a large and structurally diverse family of enzymes. The conserved catalytic domain held in common by each member of this family is a self-contained 250-300 amino acid unit bearing sixteen highly conserved linear sequence elements, several of which have been shown to be important to the catalytic activity of this domain. The enzymic activity of the PTKs is clearly an evolutionarily successful theme, and at least 10 distinct morphotypes have been described. Many of these resemble cell surface receptors for growth factors, and for a small sub-set of these receptors a ligand has been discovered. The remainder are located intracellularly and presumably sense and respond to appropriate metabolic cues by exerting their physiologically powerful enzymic activity. A detailed examination of the structure/function relationships of the PTKs and their catalytic domains is particularly revealing in trying to establish the roles that these proteins play in signal transduction in eukaryotic cells.