J. Neurochem. (2012) 122, 4–18. Abstract Immunophilin is the collective name given to a family of proteins that bind immunosuppressive drugs: Some immunophilins are Hsp90‐binding cochaperones that affect steroid receptor function. Mood and anxiety disorders are stress‐related diseases characterized by an impaired function of the mineralocorticoid and glucocorticoid receptors, two of the major regulatory elements of the hypothalamus‐pituitary‐adrenocortical axis. Genetic variations of the FK506‐binding protein of 51‐kDa, FKBP51, one of the immunophilins bound to those steroid receptor complexes, were associated with the effectiveness of treatments against depression and with a major risk‐factor for the development of post‐traumatic stress disorders. Interestingly, immunophilins show polymorphisms and some polymorphic isoforms of FKBP51 correlate with a greater impairment of steroid receptor functions. In this review, we discuss different aspects of the role of FKBP51 in such steroid receptor function and the impact of genetic variants of the immunophilin on the dysregulation of the stress response.

Cytoskeletal structure is continually remodeled to accommodate normal cell growth and to respond to pathophysiological cues. As a consequence, several cytoskeleton-interacting proteins become involved in a variety of cellular processes such as cell growth and division, cell movement, vesicle transportation, cellular organelle location and function, localization and distribution of membrane receptors, and cell-cell communication. Molecular chaperones and immunophilins are counted among the most important proteins that interact closely with the cytoskeleton network, in particular with microtubules and microtubule-associated factors. In several situations, heat-shock proteins and immunophilins work together as a functionally active heterocomplex, although both types of proteins also show independent actions. In circumstances where homeostasis is affected by environmental stresses or due to genetic alterations, chaperone proteins help to stabilize the system. Molecular chaperones facilitate the assembly, disassembly and/or folding/refolding of cytoskeletal proteins, so they prevent aberrant protein aggregation. Nonetheless, the roles of heat-shock proteins and immunophilins are not limited to solve abnormal situations, but they also have an active participation during the normal differentiation process of the cell and are key factors for many structural and functional rearrangements during this course of action. Cytoskeleton modifications leading to altered localization of nuclear factors may result in loss- or gain-of-function of such factors, which affects the cell cycle and cell development. Therefore, cytoskeletal components are attractive therapeutic targets, particularly microtubules, to prevent pathological situations such as rapidly dividing tumour cells or to favor the process of cell differentiation in other cases. In this review we will address some classical and novel aspects of key regulatory functions of heat-shock proteins and immunophilins as housekeeping factors of the cytoskeletal network.

Membrane overexpression of ErbB-2/HER2 receptor tyrosine kinase (membrane ErbB-2 (MErbB-2)) has a critical role in breast cancer (BC). We and others have also shown the role of nuclear ErbB-2 (NErbB-2) in BC, whose presence we identified as a poor prognostic factor in MErbB-2-positive tumors. Current anti-ErbB-2 therapies, as with the antibody trastuzumab (Ttzm), target only MErbB-2. Here, we found that blockade of NErbB-2 action abrogates growth of BC cells, sensitive and resistant to Ttzm, in a scenario in which ErbB-2, ErbB-3 and Akt are phosphorylated, and ErbB-2/ErbB-3 dimers are formed. Also, inhibition of NErbB-2 presence suppresses growth of a preclinical BC model resistant to Ttzm. We showed that at the cyclin D1 promoter, ErbB-2 assembles a transcriptional complex with Stat3 (signal transducer and activator of transcription 3) and ErbB-3, another member of the ErbB family, which reveals the first nuclear function of ErbB-2/ErbB-3 dimer. We identified NErbB-2 as the major proliferation driver in Ttzm-resistant BC, and demonstrated that Ttzm inability to disrupt the Stat3/ErbB-2/ErbB-3 complex underlies its failure to inhibit growth. Furthermore, our results in the clinic revealed that nuclear interaction between ErbB-2 and Stat3 correlates with poor overall survival in primary breast tumors. Our findings challenge the paradigm of anti-ErbB-2 drug design and highlight NErbB-2 as a novel target to overcome Ttzm resistance.