Structure and function of the kinome-targeting Hsp90/Cdc37 molecular chaperone system

The major molecular chaperone Hsp90 and its co-chaperone Cdc37 play a critical role in supporting the structure and function of numerous cellular signaling protein kinases.  Our research is focused on understanding the molecular mechanisms behind how Hsp90/Cdc37 stimulate the maturation and folding of signaling kinases and how they recognize them.  Furthermore, we aim to study the regulation of Hsp90 and Cdc37 in cells, with a particular focus on their post-translational modification.

The Hsp90 inhibitor geldanamycin and its derivatives bind to and inhibit Hsp90, leading to inactivation of various Hsp90-dependent protein kinases.  This unique property of Hsp90 inhibitors allows for the simultaneous suppression of multiple Hsp90/Cdc37-client kinases, making them a versatile option for treating cancer.  In contrast, conventional single kinase-targeting therapy often leads to drug-resistance issues.  Targeting the Hsp90-Cdc37 interface is also a promising approach for achieving simultaneous suppression of multiple signaling pathways supported by signaling protein kinases.

Function and regulation of DYRK family protein kinases

CK2 (formerly called as casein kinase II) is one of the earliest identified protein kinases.  Unlike other signaling protein kinases, CK2 displays constitutive protein kinase activity toward many substrates, regardless of specific upstream signals or low molecular weight second messengers.  However, CK2 activity is often observed to be elevated in malignant cells, and increased CK2 activity has been linked to cancer development.  Thus, CK2 is believed to play a role in regulating cell proliferation and cell death in tumors.

Our research focuses on the regulatory mechanisms, cellular substrates, and physiological functions of CK2.  A special focus is on the phosphorylation of Hsp90, Cdc37, a kinase-targeting molecular chaperones, and FKBP52, a steroid hormone receptors-targeting Hsp90 co-chaperone, by CK2.  In particular, CK2-dependent phosphorylation of Cdc37 on Ser13 is of critical importance for the client kinase recognition by Cdc37, giving a pivotal importance of the CK2-Cdc37-Hsp90 axis for regulating wide array of signaling protein kinases.  By understanding these regulatory mechanisms in more detail, we hope to gain new insights into the role of CK2 in cancer and other diseases, and to develop new therapies that target this important kinase.

Structure and function of a WD40-repeat protein DCAF7/WDR68

WD40 repeat proteins are characterized by a sequence consisting of approximately 40 amino acids, which includes a Trp(W)-Asp(D) motif.  These proteins are involved in cellular signal transduction by providing a molecular hub for efficient and specific protein-protein interactions.  Our research focuses on the structure and function of the WD40 repeat protein DCAF7/WDR68, which we have identified as the most major binding partner for DYRK1A kinase.

In addition to DYRK1A, we have identified several other interaction partners for DCAF7/WDR68, including the major molecular chaperone TRiC/CCT and FAM53C.  Studying the functional significance of these protein-protein interactions may reveal new insights into the physiological role of DCAF7/WDR68 in cellular signaling pathways.

One remarkable feature of DCAF7/WDR68 is its highly conserved amino acid sequence between species.  In fact, the protein shows complete conservation of its 342 amino acids between human and chicken, a very rare case.  Our future work will investigate the structural and evolutionary factors that have led to this exceptional conservation of DCAF7/WDR68.

Protein quality control and phosphorylation of a microtubule-binding protein MAPT/Tau

MAPT/Tau is a protein that binds to tubulin and promotes the stability of cytoskeleton microtubules within cells.  In neurodegenerative disorders such as Alzheimer’s disease, MAPT/Tau is hyperphosphorylated and forms fibrous aggregates that contribute to neuronal cell death and development of dementia.  Therefore, understanding the phosphorylation-dependent structural and functional changes of MAPT/Tau protein is crucial.

MAPT/Tau interacts with several molecular chaperones, including Hsp90, Cdc37, and FKBP52, but the functional relevance of these interaction remains largely unknown.  In addition, DYRK1A, a kinase involved in Down syndrome, phosphorylates MAPT/Tau on Thr212.  Our aims to elucidate the physiological importance of the interaction between MAPT/Tau and molecular chaperones, as well as the role of DYRK1A-dependent phosphorylation of MATP/Tau.

The results of our study will provide new insights into the molecular mechanism underlying Alzheimer’s disease and also the early onset of Alzheimer disease in Down syndrome patients.  By shedding light on the functional significance of MAPT/Tau interactions and phosphorylation, we hope to contribute to the development of new therapies for these debilitating disorders.

Structure and function of a protein kinase MOK, a member of MAP kinase superfamily.

MOK is a Ser/Thr protein kinase that we previously identified and cloned.  The catalytic kinase domain of MOK shares significant similarity with MAP kinases and cyclin-dependent kinases, indicating that MOK likely plays a critical role in cellular signaling.  However, the physiological role and regulatory mechanism of MOK remain largely unknown.  Recent studies in model organisms suggest that MOK is involved in regulating cilia formation.

Our research focuses on understanding the structure and function of MOK in mammalian cells.  We seek to determine how MOK activity is regulated, which substrates are phosphorylated by MOK, and which binding partners are associated with MOK in cells.  We have identified major molecular chaperones Hsp90 and Cdc37 as specific binding proteins for MOK and are continuing to identify additional MOK-binding partners.

Malformation of cilia is associated with several human diseases known as ciliopathies.  Thus, elucidating the structure, function, and regulatory mechanisms of MOK will provide crucial insights into the molecular mechanisms underlying human ciliopathies.