RESUMO
Activated Cdc42-associated kinase (ACK) is an oncogenic nonreceptor tyrosine kinase associated with poor prognosis in several human cancers. ACK promotes proliferation, in part by contributing to the activation of Akt, the major effector of class 1A phosphoinositide 3-kinases (PI3Ks), which transduce signals via membrane phosphoinositol lipids. We now show that ACK also interacts with other key components of class 1A PI3K signaling, the PI3K regulatory subunits. We demonstrate ACK binds to all five PI3K regulatory subunit isoforms and directly phosphorylates p85α, p85ß, p50α, and p55α on Tyr607 (or analogous residues). We found that phosphorylation of p85ß promotes cell proliferation in HEK293T cells. We demonstrate that ACK interacts with p85α exclusively in nuclear-enriched cell fractions, where p85α phosphorylated at Tyr607 (pTyr607) also resides, and identify an interaction between pTyr607 and the N-terminal SH2 domain that supports dimerization of the regulatory subunits. We infer from this that ACK targets p110-independent p85 and further postulate that these regulatory subunit dimers undertake novel nuclear functions underpinning ACK activity. We conclude that these dimers represent a previously undescribed mode of regulation for the class1A PI3K regulatory subunits and potentially reveal additional avenues for therapeutic intervention.
Assuntos
Fosfatidilinositol 3-Quinases , Proteínas Tirosina Quinases , Núcleo Celular/enzimologia , Células HEK293 , Humanos , Fosfatidilinositol 3-Quinases/metabolismo , Fosforilação , Multimerização Proteica , Proteínas Tirosina Quinases/metabolismo , Transdução de SinaisRESUMO
RbAp46 and RbAp48 (pRB-associated proteins p46 and p48, also known as RBBP7 and RBBP4, respectively) are highly homologous histone chaperones that play key roles in establishing and maintaining chromatin structure. We report here the crystal structure of human RbAp46 bound to histone H4. RbAp46 folds into a seven-bladed beta propeller structure and binds histone H4 in a groove formed between an N-terminal alpha helix and an extended loop inserted into blade six. Surprisingly, histone H4 adopts a different conformation when interacting with RbAp46 than it does in either the nucleosome or in the complex with ASF1, another histone chaperone. Our structural and biochemical results suggest that when a histone H3/H4 dimer (or tetramer) binds to RbAp46 or RbAp48, helix 1 of histone H4 unfolds to interact with the histone chaperone. We discuss the implications of our findings for the assembly and function of RbAp46 and RbAp48 complexes.
Assuntos
Proteínas de Transporte/química , Histonas/química , Chaperonas Moleculares/química , Proteínas Nucleares/química , Sequência de Aminoácidos , Sítios de Ligação , Proteínas de Transporte/metabolismo , Histonas/metabolismo , Humanos , Modelos Moleculares , Chaperonas Moleculares/metabolismo , Dados de Sequência Molecular , Proteínas Nucleares/metabolismo , Ligação Proteica , Proteína 7 de Ligação ao Retinoblastoma , Homologia de Sequência de AminoácidosRESUMO
Frostbite is a particularly severe form of cold-induced injury that most frequently causes tissular damage in acral parts (hands and feet) and usually involves a small extension of the TBSA. Here, we present a rare case of frostbite affecting a large area (27%), which was successfully treated in a similar way to a thermal burn injury.