** Image-sharing platform Pinterest's PINS.N shares rise 5.5% to $21.80

** Co expands collaboration with Amazon Web Services, including a $4 bln commitment for cloud services through 2031

** Amazon.com's AMZN.O cloud computing unit to provide PINS with its custom chip processors, including Graviton and Trainium, to help scale its AI initiatives

** AMZN up ~2% to $254.90

** YTD, PINS has fallen 15.8%, while AMZN has gained 10.4%