The SH2-SH3 adaptor protein Crkl has been implicated in the signal transduction pathways of several membranebound receptors. Tyrosine phosphorylation of proteins associated with such signalling complexes can generate binding sites for the Crkl SH2-domain and can recruit proteins constitutively bound to Crkl via the Crkl SH3 domain into such complexes. In the current study we show that Crkl, but only a minor amount of the related Crk, form constitutive complexes in vivo with guanine nucleotide exchange factor C3G in 3T3 ®broblasts. Adhesion of both normal and transformed cells to ®bronectin or other extracellular matrix proteins consistently induces the tyrosine-phosphorylation of C3G. Adhesion-induced tyrosine phosphorylation of C3G is dependent on an intact cytoskeleton and peaks at 5 ± 10 min after attachment. In contrast, 3T3 cells stably transfected with Bcr/Abl P210 show a prominent reduction in the amount of C3G complexed to Crkl and do not exhibit tyrosine-phosphorylation of C3G upon spreading and attachment. These data establish that integrin-mediated cell adhesion results in Crkl-mediated tyrosine phosphorylation of C3G, a pathway which can be disrupted by Bcr/Abl.

Here we report the identification of prominently tyrosine-phosphorylated proteins with a molecular mass of approximately 110 kDa, which bind specifically to the Crkl SH2 domain in leukemic tissues of P190BCR/ABL transgenic mice. We demonstrate that these proteins are identical to Hef1/Cas-L, which is related to p130Cas . The proto-oncoprotein p120Cbl and Hef1, but not p130 Cas , were detectably phosphorylated on tyrosine in P190Bcr/ Abl-expressing leukemic cells and were found in complex with Crkl, showing the existence of protein complexes in P190Bcr/Abl leukemic cells, consisting of P190Bcr/Abl, Crkl, and Hef1 or p120Cbl . This supports a model in which Crkl acts as mediator between Bcr/Abl and downstream effectors. Since Hef1 is involved in the ␤ 1 -integrin signaling pathway, our study demonstrates that Bcr/Abl could specifically interfere with normal ␤ 1 -integrin signaling.Several experimental mouse models have been developed to investigate the oncogenic action of Bcr/Abl, which is causative of the development of chronic myeloid leukemia (CML) 1 and Philadelphia-positive (Ph ϩ ) acute lymphoblastic leukemia (ALL), in vivo. Transgenic P190BCR/ABL mice reproducibly develop lymphoblastic leukemia/lymphoma involving cells of pre-B-cell origin or their progenitors (1, 2). Established transgenic mice strains expressing P190Bcr/Abl provide an unlimited source and unique opportunity for studying the signal transduction pathways affected by the Bcr/Abl oncoprotein in vivo.The tyrosine kinase activity located in the Abl segment of Bcr/Abl is dramatically increased (3), and this is critical for its transforming capacity. Although it remains unclear which intracellular signaling pathways are crucial to the in vivo oncogenic activity of Bcr/Abl, numerous signaling proteins have been implicated by studies involving patient-derived cell lines or stably transfected cells transformed by Bcr/Abl. However, only few signaling proteins are tyrosine-phosphorylated by Bcr/ Abl or in complex with Bcr/Abl in leukemic cells isolated directly from Ph ϩ patients, indicating the importance of studying the molecular mechanisms behind Bcr/Abl-induced leukemogenesis in an in vivo context. Signaling proteins shown to be affected by Bcr/Abl include p130Cas (4), p120 CBL (5), p68 paxillin (6), Grb-2 (7), p62 Dok (8) and p39 Crkl (9 -11). The human Crkl protein has a high degree of homology with the adaptor protein Crk (12, 13). Crkl consists of an SH2 and two SH3 domains in the absence of other functional motifs. It is ubiquitously expressed and tyrosine-phosphorylated abundantly during early embryogenesis, but tyrosine phosphorylation is very restricted in adult tissues (14). We and others have demonstrated that Crkl is constitutively tyrosine-phosphorylated in CML and ALL patient material containing an active Bcr/Abl protein (e.g. chronic and blast phase samples) but not in remission-stage samples or in several types of leukemia lacking Bcr/Abl (9 -11). Moreover, it is also abnormally tyrosine-phosphorylated in leukemic samples of P190-an...

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This document presents a set of Session Initiation Protocol (SIP) user requirements that support communications for deaf, hard of hearing and speech-impaired individuals. These user requirements address the current difficulties of deaf, hard of hearing and speech-impaired individuals in using communications facilities, while acknowledging the multi-functional potential of SIP-based communications.

Status of This MemoThis memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. AbstractThis document lists the essential requirements for real-time Textover-IP (ToIP) and defines a framework for implementation of all required functions based on the Session Initiation Protocol (SIP) and the Real-Time Transport Protocol (RTP). This includes interworking between Text-over-IP and existing text telephony on the Public Switched Telephone Network (PSTN) and other networks.