I'm a linguist not a historian, but I'd like to urge caution in the terms used here. "Proto-Indo European" is not a designation of a cultural or geographical entity, but a historical linguistics term that attests a description of a variety of related language precursors to Indo-European languages that share certain feature sets. This is an attested language group with demonstrably shared features of distal languages, including (historically - as in, it was originally "designed" by specialists in the following languages) Sanskrit, Greek, Latin etc., and this group of languages is not, by extension, a cultural group.

Although it's easy to use it as shorthand for the range of cultural and/or (we don't know) ethnic groups of (presumed) steppe warriors (or farmers, or pastoralists, depending on the academic), it's simply a construct that places all our linguistic knowledge of these early migrations (with a thin veneer of archaeological possibilities) into one convenient designation - e.g. all the lexicon for wheels and animals, and the flora and fauna that might have been encountered during the movement from east to west. One theory and a good initial exposure to these ideas is the "Kurgan" culture, which parallels the popular imagination and works as a way of explaining these shared influences. I don't cite any sources because it's not a primarily academic endeavor at this point - it's all very post-hoc. As mentioned above many question the type of language contact that occurred and so suggest much slower, more gradual population expansion scenarios than the popular "conqueror" mold.

So, your question of influence is incredibly difficult to answer without controversy in anthropology and linguistics, but it's important to recognize that the "indo-euorpeans" ('proto' is a technical term in historical linguistics) were not a group in the way that, say, the Mongols (or the Romans, or even the Crusaders etc.) were. We can cite what certain cultures might have been doing in areas that may have had early IE languages, but it wasn't likely monolithic, and we can't be sure of the dates or the timelines.