SP1 and acute lymphoblastic leukemia: Altogether, these results show that β-Arrestin1 increases the P300-Sp1 complex and the binding of P300-Sp1 to hTERT promoter, upregulates hTERT transcription, increases telomerase activity, and extends telomere length, thus, postponing cell senescence and changing the cell fate of B-ALL LICs (Figure 5g).