Well you can either mean maya time is at 280 and then starts to play:
in AE make sure image sequence is on
rmb image number, choose edit expression
change the expression to:
.frameExtension= frame<280? 0 : frame-280;
OR you want the movie to start at 280 at frame 0:
same as above expression is just
.frameExtension= frame+280;
If you really wanted to know the MEL (doesn't sound like it, most poeple who dont know mel use it as a wide umbrella for anything at all in maya. In this case expressions, which are NOT mel as such it just parses mel.) see what maya echoed in the script editor after you did the above.
PS: im not entirely sure what to make out of your question tough, its amazing. 2 sentences and already its exposing me to 3 seeds of bossibly big misunderstanding failure. Congratulations, best WTF? this quarter
Dont take that personally im well aware thet you dont care to know how things work. Theese things happen. If you just in case ARE interested let me know.