Human immunodeficiency virus (HIV) uses kinases such as Pak1 and macropinocytosis for a productive infection. Recently dynein light chain I (DLC1), a component of the dynein motor, was identified as a Pak1 substrate and interacted with the C-terminal region of DLC1 (aa 61-89). The dynein motor is implicated in retrograde transport, also of HIV, to the nucleus. It is known that DLC1 is important in macropinocytosis, and anti-dynein antibodies inhibit a productive HIV infection. Here, we show that in Hela-p-gal cells macropinocytosis was effectively blocked by a peptide spanning the C-terminal 19 amino acids of DLCI. We also found that the DLC1 peptide was capable of inhibiting the early entry steps of HIV, and the DLCI peptide efficiently inhibited a productive HIV infection, and cooperated with the anti-HIV activity of CD4 antibodies. Taken together, the potentially therapeutic DLC1 peptide represents an interesting class of HIV inhibitors, targeting an essential cellular component for HIV infection. Our findings raise the possibility that the use of a DLC1 peptide in combination with currently used anti-HIV agents, might offer additional arsenal against HIV infection in human cells. (C) 2007 Elsevier Inc. All rights reserved.