The cellular process of autophagy (literally “self-eating”) is important for maintaining the homeostasis and bioenergetics of mammalian cells. Two of the best-studied mechanisms of autophagy are macroautophagy and chaperone-mediated autophagy (CMA). Changes in macroautophagy activity have been described in cancer cells and in solid tumors, and inhibition of macroautophagy promotes tumorigenesis. Because normal cells respond to inhibition of macroautophagy by up-regulation of the CMA pathway, we aimed to characterize the CMA status in different cancer cells and to determine the contribution of changes in CMA to tumorigenesis. Here, we show consistent up-regulation of CMA in different types of cancer cells regardless of the status of macroautophagy. We also demonstrate an increase in CMA components in human cancers of different types and origins. CMA is required for cancer cell proliferation in vitro because it contributes to the maintenance of the metabolic alterations characteristic of malignant cells. Using human lung cancer xenografts in mice, we confirmed the CMA dependence of cancer cells in vivo. Inhibition of CMA delays xenograft tumor growth, reduces the number of cancer metastases, and induces regression of existing human lung cancer xenografts in mice. The fact that similar manipulations of CMA also reduce tumor growth of two different melanoma cell lines suggests that targeting this autophagic pathway may have broad antitumorigenic potential.

Chaperone-mediated autophagy (CMA) is an intracellular catabolic pathway that mediates the degradation of a selective subset of cytosolic proteins in lysosomes (Dice, 2007;Cuervo, 2010;Kon and Cuervo, 2010;Orenstein and Cuervo, 2010). The term autophagy (or selfeating) is broadly used to designate the lysosomal delivery and degradation of intracellular components (Mizushima et al., 2008;Mizushima and Levine, 2010;Yang and Klionsky, 2010). Various types of autophagy coexist in almost all cells, and they can be differentiated by the mechanisms that mediate the delivery of cargo (the substrates to be degraded) to lysosomes. Macroautophagy and microautophagy are variants of the autophagic process, in which entire regions of cytosol (in 'bulk' autophagy) or selective cytosolic components (organelles, protein complexes, protein aggregates, pathogens, etc.) are sequestered in vesicular compartments. Lysosomal enzymes can gain access to the enclosed cargo through direct fusion of the vesicles with lysosomes (in macroautophagy), or by internalization of cargo-containing vesicles that form at the lysosomal membrane (in microautophagy). A third form of autophagy, solely dedicated to degradation of soluble proteins can also be detected in most cell types in mammals. This autophagic process, known as chaperone-mediated autophagy, differs from the other forms of autophagy in both the way in which cargo proteins are recognized for lysosomal delivery and the way in which these proteins reach the lysosomal lumen (Dice, 2007;Cuervo, 2010). In this article and the accompanying poster, we summarize the main steps involved in degradation of cytosolic proteins by CMA, the essential components of this pathway both in the cytosol and at the lysosomal membrane and the basis for the regulation of this autophagic process. We also include a synopsis of the described physiological functions of CMA and some (See poster insert) Degradation by the lysosomal proteases CMA is a selective form of autophagy by which single soluble proteins are directed one-by-one to lysosomes for degradation.The steps in CMA are:Validated CMA substrates

a b s t r a c tChaperone-mediated autophagy (CMA) is a lysosomal pathway that participates in the degradation of cytosolic proteins. CMA is activated by starvation and in response to stressors that result in protein damage. The selectivity intrinsic to CMA allows for removal of damaged proteins without disturbing nearby functional ones. CMA works in a coordinated manner with other autophagic pathways, which can compensate for each other. Interest in CMA has recently grown because of the connections established between this autophagic pathway and human pathologies. Here we review the unique properties of CMA compared to other autophagic pathways and its relevance in health and disease.

V gene assembly, class switch recombination, and somatic hypermutation are gene-modifying processes essential to the development of an effective Ab response. If inappropriately applied, however, these processes can mediate genetic changes that lead to disease (e.g., lymphoma). A series of control elements within the Ig H chain (Igh) locus has been implicated in regulating these processes as well as in regulating IgH gene transcription. These include the intronic enhancer (Eμ) and several elements at the 3′ end of the locus (hs1,2, hs3a, hs3b, and hs4) known collectively as the 3′ regulatory region. Although it is clear that the Eμ plays a unique role in V gene assembly, it has not been established whether there are unique functions for each element within the 3′ regulatory region. In earlier studies in mice and in mouse cell lines, pairwise deletion of hs3b and hs4 had a dramatic effect on both class switch recombination and IgH gene transcription; deletion of an element almost identical with hs3b (hs3a), however, yielded no discernible phenotype. To test the resulting hypothesis that hs4 is uniquely required for these processes, we induced the deletion of hs4 within a bacterial artificial chromosome transgene designed to closely approximate the 3′ end of the natural Igh locus. When introduced into an Ig-secreting cell line, an Igα transcription unit within the bacterial artificial chromosome was expressed efficiently and the subsequent deletion of hs4 only moderately affected Igα expression. Thus, hs4 does not play a uniquely essential role in the transcription of a productively rearranged Ig VDJCα transcription unit.