, 2010 and Kilbourn et al., 1994). It is thus impossible to strictly separate the effects of heme and hemin as their mutual balance is dynamically regulated. On the other hand, only heme can serve as a substrate of HO-1. As a hydrophobic compound, hemin inserts into plasma membranes and translocates inside the cells. Inside the cells, the free iron is released namely by the action of heme oxygenases, hydrogen peroxide

or other non-specific degradation ( Belcher et al., 2010), leading to the generation of the hydroxyl radical ( Kruszewski, 2003) and activation of the redox-sensitive transcription factor NF-κB ( Lander et al., 1993 and Pantano et al., 2006). Heme also regulates levels and targeting of key enzymes involved in heme synthesis and

degradation, non-specific synthase of 5-aminolevulinic Metabolism inhibitor acid (ALAS1), HO-1, and of oxidative PLX3397 cell line stress response genes ( Furuyama et al., 2007, Igarashi and Sun, 2006 and Mense and Zhang, 2006). In the time-course experiments presented in this paper, HA inhibited HIV-1 replication characterized by levels of p24 Ag. In similar time-course experiments, viability of the mock-infected and infected cells in the presence of HA was found comparable to the untreated mock-infected cells, while untreated infected cells succumbed to apoptosis. A long-term culture of the cells in the presence of HA in concentrations that inhibited HIV-1 replication did not therefore negatively affect cell growth and viability; on the contrary, HA protected the infected cells from dying. We cannot, though, exclude a possibility that a selection of HA-resistant cells could take place.

In contrast to the acutely infected cells, HA revealed stimulatory effects on HIV-1 provirus and “mini-virus” reactivation in ACH-2 and A2, H12 cells, respectively. In A2 and H12 cells, HA stimulated “mini-virus” reactivation even by itself, but its effects were much weaker than the effects of PMA, PHA, or TNF-α alone or in combination with HA. The overall EGFP expression as well as percentage of EGFP-positive cells were dose-dependent in all agents. During Regorafenib a 48 h-incubation period, stimulatory effects of HA and TNF-α were more or less comparable to HA and PMA in H12 cells, while A2 cells appeared to be more responsive to TNF-α (Fig. 8D). Both cell lines seemed to respond similarly to PHA. H12 cells revealed a higher background fluorescence of untreated cells than A2 cells, similarly to the published data (Blazkova et al., 2009), but in general, they responded to the individual inducers with a smaller fold-increase than A2 cells. Perhaps, the lower responsiveness of H12 cells might be due to a somewhat higher CpG methylation of the 5′ LTR region compared to A2 cells (Blazkova et al., 2009). The observed effects of PMA on the HIV-1 provirus reactivation in ACH-2 cells were biphasic, possibly due to a low concentration of PMA used.