CBP is implicated in different biological functions

CBP is implicated in different biological functions with an essential role in maintaining normal germ cells development. CBP is expressed in primordial germ cells (PGCs) and in ESCs but is highly expressed in PGCs compared with ESCs. Proper levels of CBP have been shown to be important for hematopoietic SCs; CBP deficient hematopoietic SCs fail to self-renew (Rebel et al., 2002). Interestingly, the deletion of CREB, which could affect CBP binding to DNA-associated transcription factors, results in apoptosis in numerous cell types (Zhang et al., 2002; Barton et al., 1996; Jaworski et al., 2003; Reusch and Klemm, 2002; Dworet and Meinkoth, 2006; Scobey et al., 2001). In contrast, only two studies associate DREAM with SCs. First, Sanz et al. (2001) found that DREAM regulates the expression of the apoptotic protein Hrk within the hematopoietic system. Second, Cebolla et al. (2008) implicated DREAM in the differentiation of neural progenitors into astrocytes. More recently, our team described that the loss of DREAM protects the ras gtpase from degeneration during aging (Fontan-Lozano et al., 2009). DREAM could be directing a depletion of stem/precursor cell reservoirs. This may indicate a possible relationship between DREAM and SCs; our results uncover a hitherto unknown role of DREAM in regulating human ESCs (hESCs) pluripotency and differentiation.
Materials and methods
Results
Discussion Aging is a process that depends on diverse molecular and cellular mechanisms, such as genome maintenance and inflammation. Mechanisms to maintain genomic stability are thought to counteract the aging process, whereas inflammation is considered a driving force of human aging (Troen, 2003). Organisms have different anti-aging mechanisms to maintain genome integrity, such as DNA repair and cell cycle control, and to remove and recycle heavily damaged cells from the body, such as apoptosis and cellular senescence. Even if these mechanisms may be very efficient, they cannot cope with all genomic damage, leading to a gradual accumulation of DNA damage and mutations, thus contributing to organismal aging (Garinis et al., 2008). DREAM is considered a pro-inflammatory gene (Tiruppathi et al., 2014) and has a role in the modulation of inflammatory pain (Cheng et al., 2002; Jin et al., 2012), suggesting a possible implication in the aging process. Moreover, in an in vivo study (18-month-old dream−/− mice), we found that DREAM is a key regulator of memory and brain aging; thus, DREAM could be a potential target to not only reduce pain but also to control decline of neurons in aging (Fontan-Lozano et al., 2009), indicating a possible relationship between DREAM and SCs. However, the ex vivo data presented here indicates that loss of DREAM enhanced the loss of stem cell characteristics and increased the level of some differentiation markers. Chronic inflammation has been associated with age-related decline in the function of hematopoietic SCs and tissue-specific stem/progenitor cells (Chambers et al., 2007; Lepperdinger, 2011) and has been implicated as a mediator of almost all aging-associated diseases (Gadalla et al., 2015), such as vascular diseases, diabetes, neurodegenerative diseases, and cancer (Medzhitov, 2010; Freund et al., 2010; De Martinis et al., 2005; Sarkar and Fisher, 2006). Aging is accompanied by a progressive decline in SC function, which results in less effective tissue homeostasis and repair in mammals (Jones and Rando, 2011; Capilla-Gonzalez et al., 2013). For these reasons, we checked for a possible role of DREAM in SCs. As a first approximation, we detected DREAM expression in different cell types, including hESCs, hASCs, and hBMSCs. DREAM interacted with CREB in a Ca-dependent manner, preventing CBP recruitment. We likewise detected expression of CREB and CBP in hESCs, hASCs, and hBMSCs. All these findings point toward a possible role of DREAM in SC biology. Aging of SCs leads to impaired self-renewal and aberrant differentiation potential (Jones and Rando, 2011). Mechanisms controlling self-renewal and the proliferative capacity of SCs are essential to maintaining functional SCs during aging. It remains unknown whether declines in SCs functionality during aging influences organismal longevity. To elucidate the role(s) of DREAM in SC pluripotency, we studied the inhibition effects of DREAM on spontaneous differentiation of hESCs. During spontaneous differentiation, the expression of DREAM increased, no changes were observed in CREB, and there was an increase in the expression of CBP. In addition, we detected a decrease in CBP protein and an increase of Ser133-CREB phosphorylation. It would appear that CREB is phosphorylated in response to DREAM inhibition. Although CBP recruitment is known to require phosphorylation of Ser133 in CREB, there must be additional mechanisms (perhaps further cofactor interactions) that are also required for CBP recruitment (Zhang et al., 2005; Ooi and Wood, 2008). However, we must keep in mind that CBP is essential in maintaining normal germ cell development (Elliott et al., 2007) and is necessary for neural differentiation (Rebel et al., 2002). These data could suggest the existence of mechanisms convergent on DREAM and CREB protein phosphorylation, however the role of CBP within the hESC differentiation remains to be elucidated.