harry potter - Where had Lupin taught before Hogwarts?

In Prisoner of Azkaban, when Harry, Hermione, and Ron get on the Hogwarts Express, the only nearly empty compartment they can find is the one in which Remus Lupin is sleeping. They do not recognise him:

“Who d’you reckon he is?” Ron hissed, as they sat down and slid the door shut, taking the seats furthest away from the window.
“Professor R.J. Lupin,” whispered Hermione at once.

“How d’you know that?”
“It’s on his case,” replied Hermione, pointing at the luggage rack over the man’s head, where there was a small, battered case held together with a large quantity of neatly knotted string. The name ‘Professor R.J. Lupin’ was stamped across one corner in peeling letters.

At the time this happens, the school year has not started yet, and Lupin is technically not yet their teacher (although he has of course already accepted the position at the school). Nonetheless, the name stamp on his bag includes the title ‘professor’, and is obviously not a new addition, either: it is old enough that the letters are starting to peel off.

That would imply that Lupin had earned the title of professor somewhere before the summer of 1993 when he started teaching Defence against the Dark Arts in Prisoner of Azkaban.

But where? Is there any information on whether he had at any point in the past been a teacher at Hogwarts? Or at some other school?

His Wikia article says (citing Pottermore) that after the first war, he was forced to take a series of jobs that were far below his abilities and leaving them before his coworkers found out he was a werewolf; but it says nothing about teaching.

Has JKR mentioned this at any point?

Answer

J.K. Rowling has written extensively about Remus Lupin on Pottermore (Prisoner of Azkaban - Remus Lupin) and describes Lupin's parents' courtship and marriage (Remus is a half-blood, if anyone is interested), Remus's childhood, being bitten by werewolf Fenrir Greyback and becoming a werewolf himself, his years as a student at Hogwarts, his participation as a member of the Order of the Phoenix, his hand-to-mouth existence after the first Voldemort war was over and his complicated relationship with the Wolfsbane potion (he refused to take it because sampling the potion would mean admitting to others he was a werewolf), and Dumbledore's offer of the Defence Against the Dark Arts position at Hogwarts.

J.K. Rowling does not indicate that any of Remus's odd jobs included teaching or tutoring. It appears the Hogwarts DADA position was Lupin's first teaching assignment. Dumbledore assured Remus that all the Wolfsbane potion Remus would need would be available. J.K. Rowling writes that Remus Lupin turned out to be a natural teacher with an affinity for the subject matter, but more so his students and their inner workings. I think she demonstrates this aptly in Harry Potter and the Prisoner of Azkaban (On a personal note, it was Lupin and Prisoner of Azkaban that really hooked me on the series).

_{The link goes to Pottermore, the original source of the info on Lupin. You need an account to access the info on Pottermore, but accounts are free. Just an FYI. There's also the Pottermore Wiki for verification purposes -- just be advised that it's not always 100% up to date.}