Regulation of Progenitor Cell Fusion by ABCB5 P-glycoprotein, a Novel Human ATP-binding Cassette Transporter

Abstract

Cell fusion involving progenitor cells is a newly recognized phenomenon thought to contribute to tissue differentiation. The molecular mechanisms governing cell fusion are unknown. P-glycoprotein and related ATP-binding cassette transporters are expressed by progenitor cells, but their physiological role in these cell types has not been defined. Here, we have cloned ABCB5, a rhodamine efflux transporter and novel member of the human P-glycoprotein family, which marks CD133-expressing progenitor cells among human epidermal melanocytes and determines as a regulator of membrane potential the propensity of this subpopulation to undergo cell fusion. Our findings show that polyploid ABCB5 ؉ cells are generated by cell fusion and that this process is specifically enhanced by ABCB5 Pglycoprotein blockade. Remarkably, multinucleated cell hybrids gave rise to mononucleated progeny, demonstrating that fusion contributes to culture growth and differentiation. Thus, our findings define a molecular mechanism for cell fusion involving progenitor cells and show that fusion and resultant growth and differentiation are not merely spontaneous events, but phenomena regulated by ABCB5 P-glycoprotein.Several recent reports have demonstrated that co-culture of pluripotent embryonic or mesenchymal stem cells with lineagecommitted cell types can give rise to cell hybrids as a result of cell fusion, and it has been shown that such cell hybrids can generate differentiated progeny in vitro and in vivo (1-5). These findings raise the possibility that cell fusion may represent a physiological mechanism by which endogenous progenitor cells participate in tissue plasticity and renewal. A cellular molecular marker identifying progenitor cells participating in cell fusion or associated with the regulation of cell fusion has as of yet not been identified, however. P-glycoproteins (P-gp) 1 and related members of the ABC superfamily of active transporters mediate multidrug resistance in mammalian cancers (6 -13) and serve physiologic transport (14 -21), differentiation (22, 23), and survival (24, 25) functions in nonmalignant cell types. Two known members of the ABC superfamily of transporters, ABCB1 (MDR1) P-gp and the ABCG2 (Bcrp1) transporter, are also expressed at high levels on stem and progenitor cell populations (26, 27), and the efflux capacity for the fluorescent dyes rhodamine-123 (28 -30) and Hoechst 33342 (31-34) mediated by these or related ABC transporters has been utilized for the isolation of such cell subsets. A physiologic role of ABC transporters in such progenitor cells has, however, not been defined. A recent study investigated a possible role of ABCB1 P-gp as a determinant of membrane fluidity and membrane potential, but ABCB1 P-gp was found not responsible for the plasma membrane hyperpolarization observed in multidrug resistant cells (35). Here we have cloned and characterized a novel, third member of the human P-gp family encoded on chromosome 7p21-15.3, designated ABCB5 (ATP-binding cassette, subfamily B (MDR/TAP), member ...

Melanoma stem cells: not rare, but well done

“…66 Reasoning an ABC transporter that had been newly cloned, ABCB5 (ATPbinding cassette, subfamily B, member 5), might hold the key to understanding progenitor cell fusion; it was found that ABCB5 marks CD133 þ progenitor skin melanocytes and also determines the propensity for fusion. 43 Furthermore, ABCB5 expression was detected in cells from an established human melanoma cell line. Thus, by defining a molecular mechanism for stem cell fusion that resulted in cell growth and differentiation, the stage was set for determining the potential relevance of this marker to human melanoma.…”

“…43 At the time it was known that co-culture of pluripotent embryonic and mesenchymal stem cells with lineagecommitted cell types produced hybrids as a result of cell fusion, and that these hybrids could generate differentiated progeny in vitro and in vivo. [44][45][46][47][48] Although such fusion events were thus considered to represent a model whereby progenitor cells express plasticity and renewal, the mechanism for this process was unknown.…”

“…It has been hypothesized that cancer stem cells represent a pool of resistant cells in cancer patients. 99 In melanoma, cancer stem cells have been described as chemoresistant 30,43 and immunoevasive, 103 and have been associated with metastases 147 virulence-associated phenomenon of VM. 37,38,118,123 These protective properties for the melanoma stem cell translate into tumor aggressiveness directed against the patient.…”

Co-Expression of Putative Cancer Stem Cell Markers, CD133 and Nestin, in Skin Tumors

“…CSCs have been identified in a number of cancers including acute myeloid leukaemia (AML) (Bonnet and Dick, 1997;Passegue et al, 2003), glioblastoma (Singh et al, 2003), breast (Al-Hajj et al, 2003;Ponti et al, 2005), lung (Kim et al, 2005), prostate (Collins et al, 2005), ovarian (Bapat et al, 2005), gastric (Houghton et al, 2004), esophagous ( Li et al, 2013 ), Head and Neck SCC (Satpute et al, 2013) and skin cancers (Frank et al, 2005;Monzani et al, 2007). Different markers have been identified to be expressed on melanoma stem cells (Quintana et al, 2010;Shakhova and Sommer, 2013) comprising CD20 (Fang et al, 2005) and ABC transporter family members such as MDR1, ABCG2 and ABCB5 (Frank et al, 2003;Frank et al, 2005;Monzani et al, 2007;Keshet et al, 2008;Schatton et al, 2008), CD271 (Boiko et al, 2010;Civenni et al, 2011), CD44 (Fernandez-Figueras et al, 1996, CD133 (Klein et al, 2006) and Nestin (Piras et al, 2010;Fusi et al, 2011). Among these markers, CD133 and Nestin have been described as markers of melanocytic stem cells and two of the most important surface markers with increased expression in the cancer stem cell fraction in different human malignancies, including melanoma (Klein et al, 2006;Monzani et al, 2007;Rappa et al, 2008;Al Dhaybi et al, 2010;Shakhova and Sommer, 2013).…”

Tumorőssejtek szerepe a melanoma progressziójában és heterogenitásában

“…Szintén a tumorőssejt-hipotézis mellett szól, hogy az említett sejtklónokon olyan jellegzetes sejtfelszíni markerek expresszálódnak, amelyek az embrionális vagy szomatikus őssejtekre jellemzők. A tumorőssejtek nem feltétlenül a szomatikus őssejtek onkogén transzformációjából származnak, hanem létrejöhet-nek a szöveti sejtekben bekövetkező génmutációk és génexpressziós változások következtében, vagy akár tumoros sejtek differenciált sejtekkel és őssejtekkel való fú-ziójával is [14].…”