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Enzyme
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Target Concepts:
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Query: EC:3.6.1.3 (
ATPase
)
65,361
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
Calponin is an extensively studied actin-binding protein, but its function is not well understood. Among three isoforms of calponin,
h2-calponin
is found in both smooth muscle and non-muscle cells. The present study demonstrates that epidermal keratinocytes and fibroblast cells express significant amounts of
h2-calponin
. The expression of
h2-calponin
is cell anchorage-dependent. The levels of
h2-calponin
decrease when cells are rounded up and remain low when cells are prevented from adherence to a culture dish.
h2-calponin
expression resumes after the floating cells are allowed to form a monolayer in plastic dish. Cell cultures on polyacrylamide gels of different stiffness demonstrated that
h2-calponin
expression is affected by the mechanical properties of the culture matrix. When cells are cultured on soft gel that applies less traction force to the cell and, therefore, lower mechanical tension in the cytoskeleton, the level of
h2-calponin
is significantly lower than that in cells cultured on hard gel or rigid plastic dish. Force-expression of
h2-calponin
enhanced the resistance of the actin filaments to cytochalasin B treatment. Keratinocyte differentiation is accompanied by a mechanical tension-related up-regulation of
h2-calponin
. Lowering the tension of actin cytoskeleton by inhibiting non-muscle myosin II
ATPase
decreased
h2-calponin
expression. In contrast to the mechanical tension regulation of endogenous
h2-calponin
, the expression of
h2-calponin
using a cytomegalovirus promotor was independent of the stiffness of culture matrix. The results suggest that
h2-calponin
represents a novel manifestation of mechanical tension responsive gene regulation that may modify cytoskeleton function.
...
PMID:h2-Calponin is regulated by mechanical tension and modifies the function of actin cytoskeleton. 1623 5
Calponin is an actin filament-associated regulatory protein, and its h2 isoform is expressed in lung alveolar epithelial cells under postnatal upregulation during lung development corresponding to the commencement of respiratory expansion. Consistent with this correlation to mechanical tension, the expression of
h2-calponin
in alveolar cells is dependent on substrate stiffness and cytoskeleton tension. The function of
h2-calponin
in the stability of actin cytoskeleton implicates a role in balancing the strength and compliance of alveoli. An interesting finding is a rapid degradation of
h2-calponin
in lung after prolonged deflation, which is prevented by inflation of the lung to the in situ expanded volume. Decreasing mechanical tension in cultured alveolar cells by reducing the dimension of culture matrix reproduced the degradation of
h2-calponin
. Inhibition of myosin II
ATPase
also resulted in the degradation of
h2-calponin
in alveolar cells, showing a determining role of the tension in the actin cytoskeleton. Alveolar cells statically cultured on silicon rubber membrane build high tension in the cytoskeleton corresponding to a high expression of
h2-calponin
. Chronic cyclic stretching of cells on the membrane did not increase but decreased the expression of
h2-calponin
. This finding suggests that when cellular structure adapts to the stretched dimension, cyclic relaxations periodically release cytoskeleton tension and lower the total amount of tension that the cell senses over time. Therefore, the isometric tension, other than tension dynamics, determines the expression of
h2-calponin
. The tension regulation of
h2-calponin
synthesis and degradation demonstrates a novel mechanical regulation of cellular biochemistry.
...
PMID:Cytoskeletal tension regulates both expression and degradation of h2-calponin in lung alveolar cells. 1717 89
