Misfolding of proteins plays an important part in the pathogenesis of several lung diseases. Misfolded and aggregated proteins are handled in the cell through chaperone-mediated refolding, or destroyed by proteasomal degradation. Recent evidence suggests that cells have evolved a third pathway that involves sequestration of misfolded proteins into specialized "holding stations", close to the nucleus, called aggresomes. Recognizing the importance of this topic, the NHLBI convened a workshop to review protein processing related issues. The workshop emphasized the need for understanding the nature and the role of aggresome and the cellular mechanisms of its formation. We have discovered that cells regulate inducible nitric oxide synthase (iNOS) through aggresome formation. This newly discovered iNOS aggresome is the first described occurrence of an aggresome that is not associated with protein misfolding and which we termed "physiologic aggresome". This discovery sets the stage for a unique research opportunity. Study of the physiologic aggresome should reveal a wealth of information regarding how cells regulate proteins through aggresome formation. We hypothesize that: A) iNOS physiologic aggresome shares certain features with what previously described as "pathologic" aggresome associated with misfolded proteins. Thus, pathologic aggresome may merely represent an acceleration of an established physiologic regulatory process. B) The regulation of aggresome formation in cells is linked to cell capacity to degrade proteins in a timely manner. Whenever cells sense that this capacity is likely to be exceeded due to the generation of either a misfolded protein or a large amount of a certain protein, they trigger aggresome formation. The decision of cells to resort to aggresome formation results in specific proteins migrating to participate in the formation and the regulation of the aggresome. To test these hypotheses we propose studies with the following specific aims: 1) Characterization of mechanisms of formation and regulation of iNOS aggresome. 2) Identification of proteins forming iNOS aggresome. 3) Examination of the regulation of iNOS aggresome in cells harboring misfolded mutant proteins related to lung disease such as a1-antitrypsin mutants. The rationale for the proposed studies is that once these mechanisms are understood, they would greatly increase our understanding of cellular handing of misfolded proteins. Future therapeutic strategies can be designed to regulate these cellular responses in disease states.