1. ¹Department of Pathology, University of Pittsburgh, Pittsburgh, PA, USA
2. ²Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, PA, USA
3. ³Department of Neurosurgery, University of Pittsburgh, Pittsburgh, PA, USA
4. ⁴Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA

Correspondence: Dr ME Beckner, MD, Department of Pathology, University of Pittsburgh Medical Center, 200 Lothrop Street, PUH, Room A-515, Pittsburgh, PA 15213, USA. E-mail: becknerme@upmc.edu

Received 21 April 2006; Revised 20 July 2006; Accepted 21 July 2006; Published online 11 September 2006.

Abstract

It is well accepted that dysfunction in the blood brain barrier (BBB) allows permeation of albumin from the bloodstream into astrocytic brain tumors, especially glioblastomas, the most aggressive astrocytomas. In vitro, bovine serum albumin (BSA) aids functional cell assays by maintaining cytokines and growth factors in solution and delivering its cargo of fatty acids. Earlier, we showed that BSA was prominent in lysates prepared from pseudopodia formed by U87 astrocytoma cells. The present studies investigated the association of albumin with pseudopodia formed by U87 and LN229 astrocytoma cells. With hepatocyte growth factor (HGF) stimulation, cell migration was enhanced and BSA, especially its dimerized form, was prominent in pseudopodia compared to unmigrated cells on one-dimensional gels and immunoblots. When lysates were equalized for levels of glyceraldehyde-3-phosphate dehydrogenase, the rise for BSA levels in pseudopodia vs migrated cells was comparable or greater than levels noted for established pseudopodial proteins, -actin and ezrin. The increase for dimerized BSA in pseudopodia compared to unmigrated cells was greater than the rise in levels of -actin, ezrin, HGF, and phosphorylated Met when pseudopodia were harvested from filters with 1 m pores using either cell line. Fluorescein (F)-labeled BSA co-localized with HGF on actin-rich cellular protrusions and with CM-DiI labeled pseudopodial plasma membranes. The F-BSA highlighted small, individual pseudopodial profiles more so than complex pseudopodial networks (reticulopodia) or unmigrated cells. Labeled human serum albumin also decorated pseudopodia preferentially. Albumin's association with pseudopodia may help to explain its selective accumulation in astrocytomas in vivo. The leaky BBB permits serum albumin to enter the microenvironment of astrocytomas thus allowing their invasive cells contact with serum albumin as a source of fatty acids that would be useful for remodeling cell membranes in pseudopodia. Thus, albumin potentially aids and marks invasion as it accumulates in these tumors.