| Summary: | 博士 === 長庚大學 === 生物醫學研究所 === 105 === Cell migration is very important for many physiological and pathological processes, such as embryonic development, wound healing, immune response and cancer metastasis. Nonmuscle myosin II (NM-II) is a critical motor protein complex for both cell migration and cell contraction. Incorporation of NM-II into actin filament provides a tractive force for actin retrograde flow and focal adhesion assembly.
Regulation of NM-II involves myosin filament assembly and myosin ATPase activation. In addition to proteins directly controlling NM-II assembly, several kinases are implicated in the activation of myosin ATPase through myosin regulatory light chain (MRLC) phosphorylation. Moreover, certain proteins serve as scaffolds to link NM-II and its regulatory kinases.
Although many studies reveal the mechanisms in regulating NM-II assembly and activation, regulatory components participated in these mechanisms are not well understood. Thesis presented here identified a novel actin stress fiber associated protein, LIM and calponin-homology domains 1 (LIMCH1), which could suppress cell migration and promote NM-II activity. Recruitment of LIMCH1 into contractile stress fiber displayed a complementary localization with actinin-1. More evidence demonstrated that LIMCH1 interacted with NM-IIA through its N-terminal coiled-coil domain. The head of NM-IIA was also responsible for LIMCH1 directly binding. Moreover, this interaction was not interfered with inhibition of myosin ATPase activity.
The molecular function study indicated that LIMCH1 enhanced the NM-II activity by detection of MRLC phosphorylation. Elimination of LIMCH1 expression prevented MRLC assembly (may indicate NM-II) and accelerated MRLC turnover rate. Indirect evidence showed that LIMCH1 depletion increased FAK phosphorylation, implying high adhesion turn over caused by attenuation of NM-II tension. Reduced NM-II activity in LIMCH1-depleted HeLa cell resulted in loss of actin stress fiber and focal adhesion at the center of the cell. These LIMCH1-mediated effects through regulation of NM-II activity might reflect on cell function. Loss of LIMCH1 in HeLa and J7 cell lines altered their cell morphology. In addition, cell migration was increased in LIMCH1-depleted HeLa cell; cell spreading was also promoted in this cell. Evidences provided here suggested that LIMCH1 plays a positive role for regulation of NM-II activity during cell migration.
Furthermore, combination of bioinformatics analysis and lab-created protein-protein-interaction results identified several LIMCH1 interacting proteins. Interactome confirmed that LIMCH1 was involved in cytoskeleton process. Some LIMCH1 interacting candidates implied that LIMCH1 might participate in enzyme and nucleotide regulation.
In the pathology correlation study, LIMCH1 was highly expressed in normal lung tissues, whereas LIMCH1 expression was significantly reduced in the lung cancer. Bioinformatics analysis confirmed this evidence. Therefore, LIMCH1 may be involved in the lung cancer progression.
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