Work from Nagl et al., for example, have shown that a choice in association between two different variants of a major BEZ235 subunit of the ARID protein family determines whether the SWI/SNF complex forms further associations with activator or repressor complexes. Our observation that E2F6 binds to BRG1 suggests a role for BRG1 in transcriptional repression in this context. We observed BRG1 also interacts with E2F4, another transcriptional repressor in the E2F family of proteins, when ectopically expressed in cells, although this was not observed in yeast. We speculate that the interaction between E2F4 and BRG1 may be weak and may not occur under normal physiological conditions. The observation that BRG1 is capable of binding E2F4 when overexpressed, however, is consistent with our previous observations indicating E2F4 can compensate for E2F6 in E2f6-null cells. A number of studies have implicated a role for BRG1 in E2F regulation via its interaction with other proteins, although a direct interaction between E2Fs and BRG1 has not been documented. EVI1, a DNA-binding protein that belong to the Kruppel family of proteins, interacts with BRG1 to block BRG1’s repressive regulation on E2F1 activity. Prohibitin, a potential tumor suppressor gene, recruits BRG1 for repression of E2F responsive promoters by estrogen antagonists. TopBP1, a DNA topoisomerase IIb binding protein, represses E2F1 transcription by a BRG1 dependent mechanism. Our observation that E2F6 can coimmunoprecipitate with BRG1 and its subunits, BAF155 and BAF180, suggests E2F6 can be a component of the polybromo-containing SWI/SNF complex known as PBAF under specific biological contexts. This is particularly interesting given a recently documented role for PBRM1 loss in renal and breast cancers. Our results presented here highlight diverse roles in normal homeostasis for another E2F family member that can be dictated by their interacting proteins. Although MPTP causes oxidative stress and energy depletion because of impaired mitochondrial function, recent studies suggest that MPTP also causes endoplasmic reticulum stress, a type of intracellular stress that is characterized by the accumulation of unfolded proteins in the ER. ER stress occurs when cells are in conditions such as glucose starvation, oxygen deprivation, protein modification inhibition, and disturbance of Ca2+ homeostasis. Eukaryotic cells respond to ER stress by activating a set of pathways known as the unfolded protein response. In mammals, the UPR is transmitted through 3 types of sensor proteins; double-stranded RNA-activated protein kinase –like ER kinase, inositol-requiring enzyme 1a, and activating transcription factor 6a. Ire1a and ATF6a downstream genes include molecular chaperones in the ER, such as glucose-regulated protein78, and oxygen-regulated protein 150, and ER-associated degradation molecules such as Derlins, ER degradation enhancing alpha-mannosidase-like protein, and homocysteine-inducible endoplasmic reticulum stress protein. In contrast, PERK downstream genes include eukaryotic translation initiation factor 2, which suppresses general protein synthesis to reduce protein loads into the ER, and activating transcription factor 4, which upregulates the expression of anti-oxidative genes such as heme oxygenase 1 and cystine/glutamate antiporter. PERK also upregulates the pro-apoptotic transcriptional factor C/EBP homologous protein. Cell culture models and the acute MPTP injection models.