Multifunctional structural proteins, serving as linkers or adaptors, are essential for cellular remodeling processes. The long-term objective of this proposal is to elucidate how molecular interactions of structural proteins, particularly cytoskeletal protein 4.1, contribute to cell division. Protein 4.1 is a multifunctional structural protein that in red cells integrates components crucial for regulation of red cell skeletal organization and mechanical stability. However, it is now established that protein 4.1 is expressed in non-erythroid nucleated cells as well as in erythroid cells and is detected at sites such as centrosomes, mitotic spindles and nuclei. Although the role of protein 4.1 in mature red cells is well defined, its role(s) in nucleated cells are not well understood. We reported that 4.1 is required for microtubule organization and dynamics essential for proper mitotic spindle and centrosome formation. We also showed that at least two 4.1 domains directly function in assembly of these subcellular organelles. Our central hypothesis is that protein 4.1 interactions link or integrate structural components within centrosomes and spindle poles to provide dynamic properties necessary for assembly/disassembly during cell division. To obtain a detailed understanding of the interactions and mechanisms involved, two Aims are proposed: (1) elucidate mechanisms for 4.1 regulation of microtubule dynamics and organization in mitotic spindle poles and centrosomes, (2) determine how 4.1 expression affects cell division. We anticipate that identifying functional interactions of protein 4.1 will further increase our understanding of fundamental principles of assembly and dynamics of centrosomes and mitotic spindles during cell division and differentiation. This in turn may indicate the genesis of previously unrecognized pathological consequences of 4.1 gene defects. However, our investigations will also contribute a broad perspective on molecular disease loci involving defective or deficient cytoskeletal proteins.
