In ₁-AT deficiency, a mutant form of ₁-AT polymerizes in the ER of liver cells resulting in chronic hepatitis and hepatocellular carcinoma by a gain-of-toxic function mechanism. Although some aspects of the cellular response to mutant ₁-AT Z have been partially characterized including the involvement of several proteosomal and nonproteosomal mechanisms for disposal, other parts of the cellular response pathways, particularly the chaperones with which it interacts and the signal transduction pathways that are activated, are still not completely elucidated. The ₁-AT Z molecule is known to interact with calnexin but, according to one study, it does not interact with Grp78. To carry out a systematic search for the chaperones with which ₁-AT Z interacts in the ER we used chemical cross-linking of several different genetically engineered cell systems. Mutant ₁-AT Z was cross-linked with Grp78, Grp94, calnexin, Grp170, UDP-glucose: glycoprotein glucosyltransferase (UGGT) and 2 unknown proteins of ~110-130 kDa. Sequential immunoprecipitation/immunoblot analysis and co-immunoprecipitation techniques demonstrated each of these interactions without chemical cross-linking. The same chaperones were found to interact with two non-polymerogenic ₁-AT mutants that are retained in the ER, indicating that these interactions are not specific for the ₁-AT Z mutant. Moreover, sucrose density gradient centrifugation studies suggest that ~85 % of ₁-AT Z exists in heterogeneous soluble complexes with multiple chaperones, and ~ 15 % in extremely large polymers/aggregates devoid of chaperones. Agents which perturb the synthesis and/or activity of ER chaperones, such as tunicamycin and calcium ionophore A23187, have different effects on the solubility and degradation of ₁-AT Z as well as on its residual secretion.