Type beta transforming growth factor is a potent inhibitor of XXXX megakaryocytopoiesis in vitro.

@entity1 @entity641 @entity19 @entity3019 @entity4360 @entity4383
To investigate the potential role of platelets in the inhibition of megakaryocytopoiesis, freeze-thawed extracts of @entity1 platelets were added to serumless liquid cultures of @entity19 marrow. When @entity4360 ( @entity4360 ), a marker of megakaryocytic differentiation in @entity19 , was assayed, a significant inhibition of enzymatic activity was noted in cultures containing the equivalent of greater than 5 X 10(6) solubilized platelets per milliliter. Freeze-thawed extracts of granulocytes had significantly less inhibitory effect than did platelets. @entity4383 growth factor beta ( @entity641 ), a growth factor known to be inhibitory to some cell lineages and to be found at relatively high concentrations in platelets, was then added to liquid marrow cultures. A similar inhibition of @entity4360 activity was detected when cultures were stimulated with mitogen-stimulated conditioned medium. The effect was potent with 50% inhibition of @entity4360 activity observed at 4 pmol @entity641 /L. To determine if @entity641 inhibited specifically one aspect of megakaryocytic differentiation, the factor was added to isolated single megakaryocytes in serumless culture induced by @entity3019 ( @entity3019 ) to increase in size. The number of megakaryocytes increasing in size in response to @entity3019 exposure was reduced from 68% to 20% when both factors were simultaneously added to cultures. Colony assays showed that megakaryocytic and granulocyte-macrophage colony detection was inhibited at picomolar concentrations of the factor. These data suggest that @entity641 is a potent in vitro inhibitor of the @entity19 megakaryocytic lineage, although its effects are not limited to this lineage.
