The adhesion modulation protein, AmpA localizes to an endocytic compartment and influences substrate adhesion, actin polymerization and endocytosis in vegetative Dictyostelium cells.
BMC Cell Biol 2012;
13:29. [PMID:
23126556 PMCID:
PMC3586950 DOI:
10.1186/1471-2121-13-29]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 10/22/2012] [Indexed: 11/10/2022] Open
Abstract
Background
AmpA is a secreted 24Kd protein that has pleiotropic effects on
Dictyostelium development. Null mutants delay development at
the mound stage with cells adhering too tightly to the substrate. Prestalk
cells initially specify as prespore cells and are delayed in their migration
to the mound apex. Extracellular AmpA can rescue these defects, but AmpA is
also necessary in a cell autonomous manner for anterior
like cells (ALCs) to migrate to the upper cup. The ALCs
are only 10% of the developing cell population making it difficult to study
the cell autonomous effect of AmpA on the migration of these cells. AmpA is
also expressed in growing cells, but, while it contains a hydrophobic leader
sequence that is cleaved, it is not secreted from growing cells. This makes
growing cells an attractive system for studying the cell autonomous function
of AmpA.
Results
In growing cells AmpA plays an environment dependent role in cell migration.
Excess AmpA facilitates migration on soft, adhesive surfaces but hinders
migration on less adhesive surfaces. AmpA also effects the level of actin
polymerization. Knockout cells polymerize less actin while over expressing
cells polymerize more actin than wild type. Overexpression of AmpA also
causes an increase in endocytosis that is traced to repeated formation of
multiple endocytic cups at the same site on the membrane. Immunofluorescence
analysis shows that AmpA is found in the Golgi and colocalizes with calnexin
and the slow endosomal recycling compartment marker, p25, in a perinuclear
compartment. AmpA is found on the cell periphery and is endocytically
recycled to the perinuclear compartment.
Conclusion
AmpA is processed through the secretory pathway and traffics to the cell
periphery where it is endocytosed and localizes to what has been defined as
a slow endosomal recycling compartment. AmpA plays a role in actin
polymerization and cell substrate adhesion. Additionally AmpA influences
cell migration in an environment dependent manner. Wild type cells show very
little variation in migration rates under the different conditions examined
here, but either loss or over expression of AmpA cause significant substrate
and environment dependent changes in migration.
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