Nut gives great advice (as always). Where I work one of my bosses is in charge of recruiting. Since he's super busy with client work, he's "trained" me on what he wants me to look for. Basically, I'm on the lookout for people who have worked for our competitors. I think a lot of bigger companies are like mine. They scan resumes for competitors or key words that have to do with the position. If it's not there, we send the rejection letter.
So definitely highlight the PR work in your sales job. Leave out the "sales" stuff, or put it as the last bullet point, and instead list promotions you put together, ways you were able to increase visibility for the store etc etc. Obviously you shouldn't lie, but only let them see what they care about.
Also, with cover letters, keep them SIMPLE! I can't stand digging through 10 lines of a person telling me about my company's accomplishments and standing in the world of brand strategy! I work here, I already know all that. Just introduce yourself and maybe bullet a few key accomplishments, and leave it at that.
Lastly, do not get discouraged at one reject. You will likely get many more over the years. Come try to be a dancer in NYC - it's like 50 rejections for every 1 call-back!
Good luck! We're pulling for you!