Yosuke Iwata

Biological and biochemical properties of Ret with kinase domain mutations identified in multiple endocrine neoplasia type 2B and familial medullary thyroid carcinoma.

Several mutations were identified in the kinase domain of the RET proto-oncogene in patients with multiple endocrine neoplasia (MEN) 2B, familial medullary thyroid carcinoma (FMTC) or sporadic medullary thyroid carcinoma. We introduced seven mutations (glutamic acid 768→aspartic acid (E768D), valine 804→leucine (V804L), alanine 883→phenylalanine (A883F), serine 891→alanine (S891A), methionine 918 →threonine (M918T), alanine 919→proline (A919P) and E768D/A919P) into the short and long isoforms of RET cDNA and transfected the mutant cDNAs into NIH3T3 cells. The transforming activity of the long isoform of Ret with each mutation was much higher that that of its short isoform. Based on the levels of the transforming activity, these mutant RET genes were classified into two groups; a group with high transforming activity (A883F, M918T and E768D/A919P) and a group with low transforming activity (E768D, V804L, S891A and A919P) (designated high group and low group). Interestingly, the level of transforming activity correlated with clinical phenotypes; high group Ret with the A883F or M918T mutation and low group Ret with the E768D, V804L or S891A mutation were associated with the development of MEN 2B and FMTC, respectively. In addition, we found that substitution of phenylalanine for tyrosine 905 present in the kinase domain abolished both transforming and autophosphorylation activities of low group Ret whereas it did not affect the activities of high group Ret.

Rho-dependent and -independent tyrosine phosphorylation of focal adhesion kinase, paxillin and p130 Cas mediated by Ret kinase

Glial cell line-derived neurotrophic factor (GDNF) signals through a unique receptor system that includes Ret receptor tyrosine kinase and a glycosyl-phosphatidylinositol-linked cell surface protein. In the present study, we have identified several proteins in neuroblastoma cells that are phosphorylated on tyrosine in response to GDNF. The phosphorylated proteins include focal adhesion kinase (FAK), paxillin and Crk-associated substrate, p130Cas, all of which are known to be associated with focal adhesions. Of these, paxillin and p130Cas interacted with Crk proteins in GDNF-treated neuroblastoma cells. GDNF also induced reorganization of the actin cytoskelton. Tyrosine phosphorylation of FAK, paxillin and p130Cas was inhibited by cytochalasin D or two specific inhibitors of phosphatidylinositol-3′ kinase (PI-3′ kinase), wortmannin and LY294002, indicating that their tyrosine phosphorylation depends on the formation of actin stress fiber and activation of PI-3′ kinase. In addition, phosphorylation of FAK but not of paxillin and p130Cas was markedly impaired by the Clostridium botulinum C3 exoenzyme that specifically ADP-ribosylates and inactivates Rho. These results suggested the presence of Rho-dependent and -independent signaling pathways downstream of PI-3′ kinase that mediate tyrosine phosphorylation of FAK, paxillin and p130Cas through Ret kinase.

Calcium-dependent Ret activation by GDNF and neurturin

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) define a new family of neurotrophic factors that play crucial roles in survival and differentiation of various neurons. Recent studies demonstrated that GDNF and NTN use a multicomponent receptor system in which glycosyl-phosphatidylinositol (GPI)-linked cell surface proteins and Ret receptor tyrosine kinase function as the ligand-binding and signalling components, respectively. In the present study, we investigated the role of Ca2+ ions for biochemical and biological activities of Ret because Ret has a unique structure of the extracellular domain with the cadherin-like motif. The results demonstrated that Ca2+ ions might be required for the complex formation of Ret and GDNF or NTN that induces Ret oligomerization and autophosphorylation. Full morphological differentiation of neuroblastoma cells by these neurotrophic factors was also Ca2+-dependent. These findings thus suggested that, in addition to GPI-linked cell surface proteins, Ca2+ ions are components of the signal transducing complex formed by Ret and GDNF protein family.

Implication of expression of GDNF/Ret signalling components in differentiation of bone marrow haemopoietic cells.

Glial cell line‐derived neurotrophic factor (GDNF) and neurturin (NTN) mediate their actions through a unique multicomponent receptor system composed of Ret receptor tyrosine kinase and glycosyl‐phosphatidylinositol‐linked cell surface proteins (designated GFRα‐1 and GFRα‐2). In the present study, expression of these signalling components in the process of differentiation of haemopoietic cells was investigated. Ret was expressed at variable levels in normal and malignant cells of the myelomonocyte lineage. Immunohistochemical analysis of human and mouse tissues revealed that Ret expression was increased in intermediate mature myeloid cells such as promyelocytes and myelocytes and decreased in mature granulocytes and monocytes. Consistent with this observation, when THP‐1 monocytic and HL‐60 promyelocytic leukaemia cells expressing Ret were differentiated toward macrophages or granulocytes by treatment of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) or all‐trans retinoic acid (RA), Ret expression strikingly decreased during differentiation. Expression of GDNF, NTN, GFRα‐1 and GFRα‐2 was undetectable in THP‐1 and HL‐60 cells as well as in bone marrow haemopoietic cells. In contrast, bone marrow stromal cells appeared to express GDNF, GFRα‐1 and GFRα‐2 but not Ret. These findings suggested that the interaction between stromal cells and Ret‐expressing haemopoietic cells in the bone marrow microenvironment may play a role in the differentiation of myelomonocyte‐lineage cells through activation of the GDNF/Ret signalling pathway.

Welder’s pulmonary hemosiderosis associated with systemic iron overload following exacerbation of acute adult T-cell leukemia/lymphoma

Herein, we describe a 61-year-old man diagnosed with pulmonary hemosiderosis following chemotherapy for acute adult T-cell leukemia/lymphoma (ATLL). Liver and heart biopsy confirmed hemosiderosis. ATLL progressed, and the patient died from multiorgan damage. Welders lung may have been involved in hemosiderosis and systemic iron overload. Abnormal iron metabolism or immune reactions may have influenced the clinical course, but these were not validated. Detailed analyses of family medical and lifestyle histories, and genetic examination should be performed in cases of systemic iron overload.

GM-CSF Autoantibody-positive Pulmonary Alveolar Proteinosis with Simultaneous Myeloproliferative Neoplasm

Pulmonary alveolar proteinosis (PAP) is classified as autoimmune, secondary, or genetic. We herein describe a 69-year-old man with autoimmune PAP, simultaneously diagnosed with myeloproliferative neoplasm (MPN). Two years after the diagnosis, the MPN progressed to acute myeloid leukemia, and the patient died from an alveolar hemorrhage during remission induction chemotherapy. Throughout the clinical course, no progression of PAP was observed, despite the progression to leukemia. There are few reports of autoimmune PAP with hematological malignancy, and this case demonstrated that an evaluation for GM-CSF autoantibodies is important for distinguishing the autoimmune and secondary forms of PAP, even if the patient has hematological malignancy.